Optical recording method, optical recording device, master medium exposure device, optical information recording medium, and reproducing method

ABSTRACT

An optical recording method for recording information by irradiating an optical disc medium with a modulated write pulse train of laser light variable over a plurality of power levels such that a plurality of marks are formed on the optical disc medium, edge positions of each of the marks and a space between adjacent two of the marks being utilized for recording of the information.

TECHNICAL FIELD

The present invention relates to an optical recording method, anapparatus for manufacturing a master through an exposure process(master-manufacturing exposure apparatus), an optical informationrecording medium, and a reproduction method, which utilize maximumlikelihood decoding, such as PRML, an optical recording apparatus. Moreparticularly, the present invention relates to a technique of writingunder the optimum recording conditions by making adaptive recordingcompensation at least according to the space lengths of spaces precedingand succeeding an interested mark, for the purpose of decreasing opticalintersymbol interference or thermal interference which is caused inrecording of or reproduction from a mark or pit sufficiently smallerthan a light beam spot diameter. The present invention also relates to atechnique of writing under the optimum recording conditions by makingadaptive recording compensation according to the space lengths of spacespreceding and succeeding an interested mark and, additionally, to themark lengths of marks preceding and succeeding the spaces.

In this specification, a direction in which the light beam spot at acertain position advances over an optical information recording medium(optical disc medium) due to rotation of the optical disc medium isreferred to as “posterior/succeeding”, and the opposite directionrelative to the certain position is referred to as “anterior/preceding”.

BACKGROUND ART

The conventional standards of optical disc media include BD-R, BD-RE,DVD-RAM, DVD-R, DVD-RW, CD-RW, etc. There are techniques of rewriting orincrementally writing data by emitting laser light onto optical discmedia that comply with these standards.

An example of the optical disc media is a phase change type optical discmedium. Recording of information on the phase change type optical discmedium is realized by irradiating an optical disc medium with laserlight to locally change the state of atomic bond of the material of athin film formed over a recording film surface by the injected energy ofthe laser light. The irradiation with the laser light changes thephysical state of the irradiated portion and its surrounding portion.Specifically, the crystalline state and the amorphous state havedifferent reflectances. Since a difference in the physical state leadsto a difference in reflectance, information can be read out byirradiating the disc with laser light of a sufficiently smaller powerthan that used in recording and detecting the amount of change inreflectance.

Examples of the phase change type optical disc media include writablemedia in which a GeSbTe material is used as a recording material for arecording layer as well as write-once optical disc media. PatentDocument No. 1 discloses the technique of using a material containingTe—O-M (where M is at least one of metal elements, metalloid elements,and semiconductor elements) as an example of a recording material of awrite-once optical disc medium. Te—O-M means a composite material whichcontains Te, O, and M. Immediately after the formation of a film,particles of Te, Te-M, and M are uniformly and randomly dispersedthroughout a matrix of TeO2. Irradiation of a thin film formed of thisrecording material with converged laser light causes the film to melt,so that crystals of Te or Te-M of large grain size are deposited. Thedifference of the optical state which is caused in this process can bedetected as a signal. This enables the mode of recording in whichwriting is allowed only once in the same area, so-called write-oncerecording.

In an alloy-based write-once type disc made of an inorganic material,two thin films made of different materials are combined into a laminate.These materials are heated by laser to melt, so that the materials aremixed together into an alloy, whereby record marks are formed. Anotherknown write-once optical disc medium of a different type is, forexample, such that the temperature is increased by laser irradiation tothermally decompose organic pigments of an organic pigment material, andthe change in refractive index of the decomposed part is decreased,whereby information is recorded. In the write-once optical disc mediumof this type, the principle of recording of information is such that theoptical path length of a light transmission layer appears shorter in arecorded portion than in a unrecorded portion, and as a result, thisacts like concavity/convexity pits of, for example, a read-only CD onincoming light.

In the case of mark edge recording on such a write-once optical discmedium, the optical disc medium is irradiated with laser lightconsisting of a plurality of pulse trains called “multi-pulses” suchthat the physical state of marks is changed, whereby information isrecorded. The information is read out by detecting the change inreflectance.

A conceivable measure for increasing the recording density is,typically, to decrease the length of marks and spaces which are to berecorded. However, especially when the length of a space with apreceding record mark becomes shorter, thermal interference occurs suchthat the heat at the trailing end of the recorded mark is conducted viaa space portion to affect the increase in temperature at the leading endof a succeeding mark and, on the other side, the heat at the leading endof the recorded mark affects the cooling cycle at the trailing end of apreceding mark. Even when marks and spaces formed on a track havecorrect lengths, edge positions of short marks and spaces which aredetected in reproduction are disadvantageously different from theirideal values due to the frequency characteristics of a reproductionoptical system which depend on the size of the light spot. The deviationof the detected edges from the ideal values is generally referred to as“intersymbol interference”. When the sizes of marks and spaces aresmaller than the light spot, large intersymbol interference occurs, andaccordingly, the jitter in reproduction is increased, so that the biterror rate is increased.

At the recording densities of DVDs and BDs, the sizes of marks which areto be recorded and the distance between the marks and spaces are small.As a result, the heat of laser light applied for formation of a mark notonly reaches an intended area for the mark but also is conducted viaspaces to reach the areas for preceding and succeeding marks, so thatdeformation can sometimes occur in the shapes of the interested mark andthe preceding and succeeding marks. There are known techniques capableof avoiding this problem, for example, the technique of changing theleading pulse position of a multi-pulse for forming a mark is changedaccording to the relationship of the length of the interested mark andthe length of the space with the succeeding mark, and the technique ofchanging the trailing pulse position of a multi-pulse for forming a markis changed according to the relationship of the length of the interestedmark and the length of the space with the preceding mark. Thesetechniques are techniques of recording marks with preliminarycorrections made to thermal interference of record marks. This mode ofcontrol of the write pulse position is generally referred to as adaptiverecording compensation. Patent Document No. 2 discloses such an adaptiverecording compensation method.

According to the recording method disclosed in Patent Document No. 2, awritable optical disc medium contains pre-recorded write pulse referenceconditions, by which the positional information of write pulses arespecified for respective one of the plurality of possible combinationsof the length of a mark, the length of the space with the succeedingmark, or the length of the space with the preceding mark. The recordingapparatus retrieves the write pulse reference conditions from theoptical disc medium to modify currently-effective write pulse referenceconditions such that optimum write pulse conditions are obtained.

Specifically, the positional information established for all thecombinations of the mark lengths and the space lengths of the space withthe succeeding mark included in the write pulse reference conditions, orfor all the combinations of the mark lengths and the space lengths ofthe space with the preceding mark included in the write pulse referenceconditions, are used to perform the first test writing in apredetermined track on an optical disc medium. The information recordedin the first test writing is reproduced, and the first jitter isdetected in the reproduced signal. And, a change of the firstpredetermined amount is uniformly added to the positional informationfor respective ones of all the combinations of the mark lengths and thespace lengths included in the write pulse reference conditions. Theuniformly-changed positional information is used to perform the secondtest writing in a predetermined track on the optical disc medium. Theinformation recorded in the second test writing is reproduced, and thesecond jitter is detected in the reproduced signal. In the last step,the first jitter and the second jitter are compared, and the positionalinformation which is used in the test writing that generated the smallerjitter is selected to obtain the write pulse conditions.

The recording control methods disclosed in Patent Document No. 3, PatentDocument No. 4, and Patent Document No. 5 use maximum likelihooddecoding methods, rather than utilizing the jitters in the reproducedsignal, in order to pre-estimate a signal pattern from a reproducedsignal waveform. While comparing the reproduced signal waveform and theestimated signal waveform, the reproduced signal is converted bydecoding into decoded data which has a signal path of the maximumlikelihood. This method is used to optimize the recording parameters inrecording of information such that the probability of occurrence oferrors in the process of maximum likelihood decoding is minimized.

In recent years, the higher densities of optical disc media cause thelengths of record marks to come closer to the optical resolution limit,so that increase in intersymbol interference and deterioration in SNR(Signal to Noise Ratio) become larger.

The system margin can be maintained by using a higher-order PRML method.For example, Non-Patent Document No. 1 discloses that, under thecircumstances where the optical system is such that the laser wavelengthis 405 nm and the NA (Numerical Aperture) of the objective lens is 0.85and the recording density is such that a Blu-ray Disc (BD) with thediameter of 12 cm has the capacity of 25 GB (Giga Byte) per datarecording layer, the system margin can be secured by employing the PR(1, 2, 2, 1) ML method. This document also discloses that, in the casewhere the linear density is increased by decreasing the mark length inorder to secure a storage capacity of 25 GB or larger (e.g., 30 GB or33.4 GB) per data recording layer while the same optical system is used,it is necessary to employ the PR(1,2,2,2,1)ML method.

Patent Document No. 6, Patent Document No. 7 and Patent Document No. 8disclose optimizing various recording parameters by adjusting the writepulse waveform based on the quality of composite data in accordance withthe PR(1,2,2,2,1)ML method in the case of a high recording densityoptical disc medium of 30 GB to 33.4 GB per data recording layer.

CITATION LIST Patent Literature

-   Patent Document No. 1: Japanese Laid-Open Patent Publication No.    2004-362748-   Patent Document No. 2: Japanese Laid-Open Patent Publication No.    2000-200418-   Patent Document No. 3: Japanese Laid-Open Patent Publication No.    2004-335079-   Patent Document No. 4: Japanese Laid-Open Patent Publication No.    2004-63024-   Patent Document No. 5: Japanese Laid-Open Patent Publication No.    2008-159231-   Patent Document No. 6: Japanese Laid-Open Patent Publication No.    2007-317334-   Patent Document No. 7: Japanese Laid-Open Patent Publication No.    2008-33981-   Patent Document No. 8: the specification of United States Patent    Application Publication No. 2008/0159104

Non-Patent Literature

-   Non-Patent Document No. 1: Illustrated Blu-ray Disc Reader, Ohmsha,    Ltd.

SUMMARY OF INVENTION Technical Problem

However, the techniques described in the above documents entail variousproblems as described below.

First, in a level determination method as described in Patent DocumentNo. 2 in which “0” and “1” in a reproduced signal are determinedrelative to the slice level, the amplitude of the reproduced signal isvery small in the reproduction from a mark or pit sufficiently smallerthan the light spot diameter. Therefore, signals reproduced from shortmarks and short spaces occur near the slice level and are thereforesusceptible to noise or intersymbol interference, resulting in frequentdetermination errors in the level determination.

Second, in the case of edge position adjustment of record marks which isperformed using a high-order PRML method of high reproducibility asdescribed in Patent Document No. 3, Patent Document No. 4, and PatentDocument No. 5, high density recording at the recording density of 30 GBto 33.4 GB per data recording layer is not successful under therecording conditions where the SN ratio (SNR) is maximum, resulting inreduction of the recording and reproduction margins in the whole opticaldisc system.

Third, in the recording compensation methods described in PatentDocument No. 6, Patent Document No. 7 and Patent Document No. 8, writepulse adjustment is only performed on positional informationcorresponding to the combination of the mark length of an interestedmark and the space length of a space with the succeeding interestedmark, or the combination of the mark length of an interested mark andthe space length of a space with the preceding interested mark. Thesemethods are not applicable to mark lengths which are beyond the opticalresolution that depends on the mark size and the light spot size.

As described above, none of the above conventional techniques is capableof forming or reading marks with sufficient accuracy in the case of highdensity recording which is beyond the optical resolution. As a result,sufficient data recording layer density and reliability cannot berealized.

One of the objects of the present invention is to provide an opticalrecording method and optical recording/reproduction apparatus capable ofprecise compensation for thermal interference and optical intersymbolinterference during recording in or reproduction from an optical discmedium.

Another one of the objects of the present invention is to improve thesystem margin of an optical disc medium. Specifically, in the case ofhigh linear density recording where the shortest mark length isapproximately 0.124 μm to 0.111 μm, as is the case with a Blu-ray Disc(BD) with the diameter of 12 cm and the capacity of 30 GB or 33.4 GB perdata recording layer, and such an optical system is used that thewavelength is 405 nm and the NA (Numerical Aperture) of the objectivelens is 0.85, adaptive compensation is made on the write pulseconditions of an interested mark according to the length of thepreceding or/and succeeding space and the length of the preceding or/andsucceeding mark, based on reproduced information which is maximumlikelihood decoded using the PR(1,2,2,2,1)ML method, with the view ofreducing optical intersymbol interference or thermal interference whichcan cause adverse effects in high density recording, such that highquality record marks are formed, and the system margin of the opticaldisc medium is improved.

Solution to Problem

According to an optical recording method of the present invention, anoptical disc medium is irradiated with a modulated write pulse train oflaser light variable over a plurality of power levels such that aplurality of marks are formed on the optical disc medium, edge positionsof each of the marks and a space between adjacent two of the marks beingutilized for recording of the information. The method includes the stepsof: encoding record data to generate encoded data which is a combinationof marks and spaces; classifying the encoded data according to acombination of a mark length of a mark, a space length of a first spacewith the succeeding mark, and a space length of a second space with thepreceding mark; generating a write pulse train for forming the mark, inwhich at least one of a leading end edge position, a trailing end edgeposition, and a pulse width of the write pulse train is changedaccording to a result of the classification; and irradiating the opticaldisc medium with the generated write pulse train to form the pluralityof marks on the optical disc medium.

The step of classifying may include classifying the encoded dataaccording to a combination of a mark length of a shortest mark, thespace length of the first space, and the space length of the secondspace.

The step of classifying may include classifying the encoded dataaccording to a combination of the following conditions: the mark lengthof the mark; whether the space length of the first space is “n” or “n+1or longer”; and whether the space length of the second space is “n” or“n+1 or longer”, where n is a shortest space length.

When the combination for the classification is a combination of the marklength of the mark, the space length of the first space and the spacelength of the second space, the step of classifying may includeclassifying the first space into any of predetermined M space lengthclasses (M is an integer equal to or greater than 1), and classifyingthe second space into any of predetermined N space length classes (N isan integer equal to or greater than 1, and MN). The step of classifyingmay include classifying the encoded data by space length into four spacelength classes for the first space, “n”, “n+1”, “n+2”, and “n+3 orlonger”, and two space length classes for the second space, “n” and “n+1or longer”, where n is a shortest space length, and the step ofgenerating may include changing the leading end edge position of thewrite pulse train according to the result of the classification.

The step of classifying may include classifying the encoded data byspace length into two space length classes for the first space, “n” and“n+1 or longer”, and four space length classes for the second space,“n+1”, “n+2”, and “n+3 or longer”, where n is a shortest space length,and the step of generating may include changing the trailing end edgeposition of the write pulse train according to the result of theclassification.

The step of classifying may include classifying the encoded data byspace length into four space length classes for the first space, “n”,“n+1”, “n+2”, and “n+3 or longer”, and two space length classes for thesecond space, “n” and “n+1 or longer”, where n is a shortest spacelength, and the step of generating may include changing the pulse widthof the write pulse train according to the result of the classification.

The step of classifying may include, if the mark length of the mark islonger than a shortest mark length, classifying the encoded dataaccording to at least any one of a combination of the mark length andthe first space length and a combination of the mark length and thesecond space length.

The optical recording method further includes the steps of: generatingan analog signal from the optical disc medium and generating a digitalsignal from the analog signal; reshaping a waveform of the digitalsignal; maximum likelihood decoding the reshaped digital signal based ona PRML (Partial Response Maximum Likelihood) method; generating a binarysignal which represents a result of the maximum likelihood decoding; anddetecting a shift amount in the waveform of the reshaped digital signalbased on the reshaped digital signal and the binary signal. The step ofgenerating the write pulse train may include changing, based on a resultof the detection of the shift amount, at least one of the leading endedge position, the trailing end edge position, and the pulse width ofthe write pulse train for the formation of the plurality of marks.

The step of detecting may include detecting the shift amount in thewaveform of the digital signal by a comparison of the encoded data andthe binary signal, and the step of generating the write pulse train mayinclude changing at least one of the leading end edge position, thetrailing end edge position, and the pulse width of the write pulsetrain.

The step of generating the write pulse train may include changing aposition of at least one of first to third pulse edges counted from theleading end and first to third pulse edges counted from the trailing endaccording to the result of the classification.

The following formula preferably holds:ML<λ/NA×0.26where λ is a wavelength of the laser light, NA is a numerical apertureof an objective lens, and ML is a shortest mark length.

The shortest mark length ML is preferably 0.128 μm or less.

The laser light wavelength λ is preferably in the range of 400 nm to 410nm, and the NA is preferably in the range of 0.84 to 0.86.

An optical recording apparatus of the present invention is configured torecord information by irradiating an optical disc medium with amodulated write pulse train of laser light variable over a plurality ofpower levels such that a plurality of marks are formed on the opticaldisc medium, edge positions of each of the marks and a space betweenadjacent two of the marks being utilized for recording of theinformation. The apparatus includes: an encoding section configured toencode record data to generate encoded data which is a combination ofmarks and spaces; a classification section configured to classify theencoded data according to a combination of a mark length of a mark, aspace length of a first space with the succeeding mark, and a spacelength of a second space with the preceding mark; a recording waveformgenerating section configured to generate the write pulse train forforming the mark in which at least one of a leading end edge position, atrailing end edge position, and a pulse width of the write pulse trainis changed according to the result of the classification; and a laserdriving section configured to irradiate the optical disc medium with thegenerated write pulse train to form the plurality of mark on the opticaldisc medium.

The optical recording apparatus may further include: a PRML processingsection configured to receive a digital signal generated from an analogsignal reproduce from an optical disc medium, to reshape a waveform ofthe digital signal, and to maximum likelihood decode the reshapeddigital signal based on a PRML (Partial Response Maximum Likelihood)method; a shift detecting section configured to detect a shift amount inthe waveform of the digital signal based on a binary signal whichrepresents a result of the maximum likelihood decoding and the reshapeddigital signal; and a recording compensation section configured tochange, based on a result of the detection of the shift amount, at leastone of the leading end edge position, the trailing end edge position,and the pulse width of the write pulse train for the formation of theplurality of marks.

A master-manufacturing exposure apparatus of the present invention isconfigured to record information by irradiating an optical disc mediumwhich is a resist-coated material disc with a modulated write pulsetrain of laser light variable over a plurality of power levels such thata plurality of marks are formed on the optical disc medium, edgepositions of each of the marks and a space between adjacent two of themarks being utilized for recording of the information. The apparatusincludes: an encoding section configured to encode record data togenerate encoded data which is a combination of marks and spaces; aclassification section configured to classify the encoded data accordingto a combination of a mark length of a mark, a space length of a firstspace with the succeeding mark, and a space length of a second spacewith the preceding mark; a recording waveform generating sectionconfigured to generate the write pulse train for forming the mark inwhich at least one of a leading end edge position, a trailing end edgeposition, and a pulse width of the write pulse train is changedaccording to a result of the classification; and a laser driving sectionconfigured to irradiate the optical disc medium with the generated writepulse train to form the plurality of marks on the optical disc medium.

There is provided an optical disc medium in which information is to berecorded based on the above-described optical recording method, whereinthe optical disc medium contains information about the classification ina predetermined area.

There is provided a method for manufacturing an optical disc medium inwhich information is to be recorded based on the above-described opticalrecording method, the method including the step of forming apredetermined area in which information about the classification is tobe recorded.

There is provided a method for reproducing information from an opticaldisc medium in which the marks are to be recorded based on theabove-described optical recording method, the method including the stepof reproducing the information by irradiating the optical disc mediumwith laser light.

Advantageous Effects of Invention

As described above, according to the optical recording method of thepresent invention, each mark which is to be recorded is classifiedaccording to the mark length of the mark and the lengths of itspreceding and succeeding spaces or/and the lengths of marks precedingand succeeding the spaces. The positions of pulse edges of a write pulsetrain for recording of each mark are changes according to a result ofthe classification, whereby a write pulse signal is controlled. Thisenables precise control of the leading end position or trailing endposition of a mark which is to be formed on a track of the optical discmedium. Specifically, the leading end position and the trailing endposition of the mark can be strictly controlled with a consideration foroptical intersymbol interference or thermal interference which can causeadverse effects in high density recording at a linear density that isbeyond the OTF (Optical Transfer Function) limit that depends on theshortest mark length and the light spot diameter. This increases thereliability of the recording and reproduction operations, so thathigh-density, high-capacity recording media can be realized while thesizes of the information recording apparatus and the recording media canbe decreased.

More specifically, in the case of high linear density recording wherethe shortest mark length is approximately 0.124 μm to 0.111 μm, as isthe case with a Blu-ray Disc (BD) with the diameter of 12 cm and thecapacity of 30 GB or 33.4 GB per data recording layer, and such anoptical system is used that the laser wavelength is 405 nm and the NA(Numerical Aperture) of the objective lens is 0.85, the write pulseconditions of the recording/reproduction apparatus are determined basedon information reproduced using the PR(1,2,2,2,1)ML method such thatintersymbol interference or thermal interference which can cause adverseeffects in high density recording is compensated for. As a result, highquality record marks can be formed, and the system margin of the opticaldisc medium can be improved.

Considering the effects of heat on the preceding and succeeding spaces,the anterior-side pulse edges of laser irradiation pulses, such as dTF1and dTF2, are susceptible to heat from the preceding space that is oneof the spaces closer to these pulse edges. In other words, the recordmark is susceptible to thermal interference according to the length ofthe preceding space. In an extended recording compensation method of thepresent invention, a shortest mark (2T) is recorded with recordingcompensation being made according to the lengths of the preceding andsucceeding spaces. In the case of changing the anterior-side pulseedges, such as dTF1 and dTF2, pulse width TF2 between dTF1 and dTF2, orpulse width TE2 between dTE2 and dTE3, thermal interference can bedecreased more effectively by making the recording compensation in sucha manner that the number of classes for the recording compensation as tothe length of the preceding space is larger than the number of classesfor the recording compensation as to the length of the succeeding space.Also, by decreasing the number of classes of the length of thesucceeding space, the total number of classes in the recordingcompensation table can be decreased. Thus, increases in LSI complexitycan be avoided, and the efforts in learning in the recording learningprocess can be reduced.

Considering the effects of heat on the preceding and succeeding spaces,the posterior-side pulse edges of laser irradiation pulses, such as dTE1and dTE2, are susceptible to heat from the succeeding space that is oneof the spaces closer to these pulse edges. In other words, the recordmark is susceptible to thermal interference according to the length ofthe succeeding space. In an extended recording compensation method ofthe present invention, a shortest mark (2T) is recorded with recordingcompensation being made according to the lengths of the preceding andsucceeding spaces. In the case of changing the posterior-side pulseedges, such as dTE1 and dTE2, thermal interference can be decreased moreeffectively by making the recording compensation in such a manner thatthe number of classes for the recording compensation as to the length ofthe succeeding space is larger than the number of classes for therecording compensation as to the length of the preceding space. Also, bydecreasing the number of classes of the length of the preceding space,the total number of classes in the recording compensation table can bedecreased. Thus, increases in LSI complexity can be avoided, and theefforts in learning in the recording learning process can be reduced.

By arranging the classification for the space length of a space with asucceeding interested mark and the space length of a space with thepreceding interested mark by the combination of two classes, “shortestspace length (n)” and “space length longer than the shortest spacelength (n+1 or longer)”, the thermal interference can be decreased moreeffectively. If the space with the preceding interested mark or with thesucceeding interested mark is a space of the shortest space length (n),a mark preceding or succeeding the interested mark is closer, so thatthe interested mark is particularly susceptible to heat from thepreceding or succeeding mark. In view of such, the classification isarranged by the combination of two classes, “shortest space length (n)”and “space length longer than the shortest space length (n+1 orlonger)”, and different adjustment amounts are allocated to the case of“shortest space length (n)” and the case of “space length longer thanthe shortest space length (n+1 or longer)”, so that more preciseadjustment is possible in the case of the shortest space length (n). Asa result, the thermal interference can be reduced more effectively.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram which illustrates an entire configuration of anoptical information recording/reproduction device of an embodiment ofthe present invention.

FIG. 2 is a diagram which illustrates a configuration of an opticalinformation recording medium of an embodiment of the present invention.

FIG. 3 is a timing chart regarding a recording method of an embodimentof the present invention.

FIG. 4 is a timing chart which illustrates the relationship between themark lengths and the waveforms of the write pulse train according to anembodiment of the present invention.

FIG. 5 is another timing chart which illustrates the relationshipbetween the mark lengths and the waveforms of the write pulse trainaccording to an embodiment of the present invention.

FIG. 6 is a graph which illustrates the relationship between OTF and thespatial frequency in an optical system according to an embodiment of thepresent invention.

FIG. 7 is a schematic diagram which illustrates the relationship betweenthe light spot diameter and the recorded marks according to anembodiment of the present invention.

FIG. 8 is a flowchart of an optical recording method of an embodiment ofthe present invention.

FIG. 9 is a diagram which illustrates an example of control of a writepulse train according to an embodiment of the present invention.

FIG. 10 illustrates examples of values set for the write pulseconditions according to an embodiment of the present invention.

FIG. 11 is a diagram which illustrates another example of control of awrite pulse train according to an embodiment of the present invention.

FIG. 12 illustrates examples of values set for the write pulseconditions according to an embodiment of the present invention.

FIG. 13 illustrates examples of values set for the write pulseconditions according to an embodiment of the present invention.

FIG. 14 is a diagram which illustrates state transition rules which aredefined by RLL(1,7) record code and equalization method PR(1,2,2,2,1).

FIG. 15 shows a trellis diagram which corresponds to the statetransition rules according to an embodiment of the present invention.

FIG. 16 is a graph which illustrates an example of a PR equalizationideal waveform shown in Table 1 according to an embodiment of thepresent invention.

FIG. 17 is a graph which illustrates an example of a PR equalizationideal waveform shown in Table 2 according to an embodiment of thepresent invention.

FIG. 18 is a graph which illustrates an example of a PR equalizationideal waveform shown in Table 3 according to an embodiment of thepresent invention.

FIG. 19 illustrates other examples of values set for the write pulseconditions according to an embodiment of the present invention.

FIG. 20 is a diagram which illustrates an example of a PR equalizationideal waveform shown in Table 1 and the relationship between thewaveform and a recorded mark according to an embodiment of the presentinvention.

FIG. 21 is a diagram which illustrates an example of a PR equalizationideal waveform shown in Table 2 and the relationship between thewaveform and a recorded mark according to an embodiment of the presentinvention.

FIG. 22 is a diagram which illustrates an example of a PR equalizationideal waveform shown in Table 3 and the relationship between thewaveform and a recorded mark according to an embodiment of the presentinvention.

FIG. 23 is a diagram which illustrates an example of a result ofcomparison of an error portion with a correct pattern according to anembodiment of the present invention.

FIG. 24 is a flowchart which illustrates the procedure of optimizing thewrite pulse conditions for an optical information recording mediumaccording to an embodiment of the present invention.

FIG. 25 is a diagram which illustrates an entire structure of amaster-manufacturing exposure apparatus according to an embodiment ofthe present invention.

FIG. 26 is a diagram which illustrates a stack configuration of athree-layer optical disc medium.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention are described withreference to the accompanying drawings. The embodiments are describedwith examples of a write-once, phase-change type optical disc medium(especially, BD-R (write-once Blu-ray Disc)) used as a recording medium.Note that this does not mean that the recording medium is limited to anyparticular type. The type of the recording medium is nonlimiting so longas it is of such a type that information is recorded by injecting energyinto the recording medium to form marks or pits which have differentphysical properties from unrecorded part. For example, the techniquesdescribed herein are commonly applicable to rewritable optical discmedia (e.g., BD-REs (rewritable Blu-ray Discs)). The techniquesdescribed herein are also commonly applicable to heat-mode recording onan inorganic resist coating, as is the case with a master-manufacturingexposure apparatus called a PTM (Phase Transition Mastering) apparatusthat is employed for manufacture of a read-only disc consisting of asubstrate with concavity/convexity pits and a reflection film formedthereover.

Examples of the major optical conditions and disc configuration employedin a recording method of the present invention are as follows:

-   -   laser light: in the wavelength range of 400 nm to 410 nm, e.g.,        at 405 nm;    -   objective lens: in the NA range of 0.84 to 0.86, e.g., NA=0.85;    -   track pitch: 0.32 μm; thickness of cover layer on which laser is        incident: 50 μm to 110 μm; shortest mark length of optical disc        medium (2T): 0.111 μm to 0.124 μm, e.g., 0.111 μm (this also        applies to the shortest space); and    -   modulation method for modulation data which is to be recorded:        17PP modulation.

In the case of recording with such a line density that theaforementioned shortest mark length is 0.111 μm, the storage capacityper data recording layer of an optical disc medium with the diameter of12 cm is approximately 33.4 GB. When this is applied to a 3-layer disc,the total storage capacity of the disc is approximately 100 GB. Whenthis is applied to a 4-layer disc, the total storage capacity of thedisc is approximately 134 GB. The description below is provided on theassumption that the shortest mark length is 0.111 μm. Strictly, thisvalue is 0.11175 μm, which is ¾ of the shortest mark length of BDs,0.1490 μm. Note that the concept of the present invention is not limitedto this value.

In the case of recording with such a line density that the shortest marklength is 0.116 μm, the storage capacity per data recording layer of anoptical disc medium with the diameter of 12 cm is approximately 32 GB.When this is applied to a 3-layer disc, the total storage capacity ofthe disc is approximately 96 GB. When this is applied to a 4-layer disc,the total storage capacity of the disc is approximately 128 GB.

Under the same conditions, when the shortest mark length is 0.124 μm,the storage capacity per data recording layer is 30 GB. When this isapplied to a 3-layer disc, the total storage capacity of the disc isapproximately 90 GB. When this is applied to a 4-layer disc, the totalstorage capacity of the disc is approximately 120 GB.

The speed of recording is assumed to be, for example, twice that of a BDwith the channel rate of 132 MHz (Tw=7.58 ns).

FIG. 1 shows an example of the entire configuration of an opticalrecording/reproduction device of the present invention. The opticalrecording/reproduction device includes a light emitting section 102, apreamplifying section 103, a waveform equalizing section 105, a PRMLprocessing section 108, an edge shift detecting section 109, a writepulse condition calculating section 110, a recording pattern generatingsection 111, a recording compensation section 112, and a laser drivingsection 113. The functions of respective ones of these components aredescribed in conjunction with a reproduction process and a recordingprocess of the optical recording/reproduction device which will bedescribed later.

Note that FIG. 1 shows an optical disc medium 101 which is an opticalinformation recording medium, although the optical disc medium 101 maynot be a constituent of the optical recording/reproduction device.

FIG. 2 shows the data structure of the optical disc medium 101. Theoptical disc medium 101 includes, from the outer perimeter to the innerperimeter, a data area 1001, a recording condition learning area 1002for learning of the recording conditions, and an initial value storagearea 1003 on the inner side of the recording condition learning area.

The data area 1001 is an area used for a user to actually store data inthe optical disc medium. The recording condition learning area 1002 isan area used for test recording which is carried out before actualrecording of data in the user area for correction of errors in recordingpower and write pulse conditions which would be caused due to startup ortemperature variation. The initial value storage area 1003 is aread-only area which contains information preset to each disc, such asrecommended values for the recording power, recommended values for thewrite pulse conditions, the linear velocity of recording, the disc ID,etc. These pieces of information are recorded in the form of a moldedstructure on the disc substrate using, for example, directions of trackwobbling as a recording unit.

Hereinafter, the process of reproducing data from the optical discmedium 101 is described.

The light emitting section 102 is, for example, an optical pickupincluding a laser diode (LD) that is configured to emit a light beamonto the optical disc medium 101.

The optical pickup emits a light beam output from the laser diode onto asurface of an optical disc medium and receives reflected light. Thereceived light is converted by a photodetector to an electric signalwhich is an analog reproduction signal. The analog reproduction signalis converted to a digital signal by the preamplifying section 103, anAGC section 104, the waveform equalizing section 105, and an A/Dconversion section 106. The digital signal is sampled by a PLL (PhaseLocked Loop) section 107 in clock cycles. The digital signal is input tothe PRML (Partial Response Maximum Likelihood) processing section 108.The PRML processing section 108 includes a maximum likelihood decodingsection, for example, a Viterbi decoding section, which is configured tomaximum likelihood decode the digital signal to generate a binary signalthat represents a result of the maximum likelihood decoding. The binarysignal is input to a shift detecting section 109.

Next, the process of recording data in an optical disc medium isdescribed. In a recording (writing) operation, the pattern generatingsection 111 outputs an arbitrary code sequence in the form of an NRZI(Non Return to Zero Inversion) signal. The write pulse conditioncalculating section 110 establishes the write pulse conditions in therecording compensation section 112 according to a calculation result.The laser driving section 113 drives the laser diode provided inside thelight emitting section 102 according to a signal of write pulse trainthat is converted based on the NRZI signal to record data at desiredpositions on the optical disc medium with varying recording power of thelaser light.

FIGS. 3( a)-(f) are charts that illustrate marks and spaces of a recordcode sequence, and an example of a write pulse train generatingoperation for recording the marks and spaces in this opticalrecording/reproduction device. FIG. 3( a) shows a waveform of areference time signal 1201 which serves as a time reference for therecording operation. The reference time signal 1201 is a pulse clockwith a period of Tw. FIG. 3( b) shows an NRZI (Non Return to ZeroInverted) signal which is a record code sequence generated by therecording pattern generating section 111. Here, Tw is a detection windowwidth which is the minimum unit of changes in mark length and spacelength in the NRZI 1202.

FIG. 3( c) shows an image of marks and spaces actually recorded on theoptical disc medium. The spot of the laser light scans the marks andspaces of FIG. 3( c) from left to right. For example, a mark 1207corresponds to “1”-level in the NRZI signal 1202 on a one-on-one basisand is formed so as to have a length proportional to that period.

FIG. 3( d) shows a count signal 1204. The count signal 1204 counts thetime from the leading ends of the mark 1207 and the space 1208 by theunits of Tw.

FIG. 3( e) is a schematic diagram of a classification signal 1205 in thepulse condition calculating section 110. In this example, encoded datais classified according to a combination of five values, including themark length of each mark, the space lengths of spaces with the precedingand succeeding mark, and the mark lengths of marks with the precedingspace and succeeding space. Here, the encoded data refers to record datawhich is encoded by a combination of marks and spaces. As for theclassification, for example, “3-4-5-2-6” in FIG. 3( e) means that: amark of runlength 5Tw has a preceding 4Tw space; there is a mark ofrunlength 3Tw with the preceding 4Tw space; the mark of runlength 5Twhas a succeeding 2Tw space; and there is a mark of runlength 6Tw withthe preceding 2Tw space. Note that Tw is sometimes abbreviated as “T”,e.g., “2T”, “3T”. The space length is sometimes identified by suffix“s”, e.g., “4Ts”. The mark length is sometimes identified by suffix “m”,e.g., “2Tm”.

FIG. 3( f) shows the waveform of a write pulse signal which correspondsto the NRZI signal 1202 of FIG. 3( b). This waveform is an example of anoptical waveform which is actually recorded. The write pulse signal 1206is generated with reference to the count signal 1204, the NRZI signal1202, the classification signal 1205, and a recording compensation tabledata output from the write pulse condition calculating section 110.

Note that, in this embodiment, the classification signal of FIG. 3( e)is classified according to a combination of the five values, includingthe mark length of each mark, the space lengths of spaces with thepreceding and succeeding mark, and the mark lengths of marks with thepreceding space and succeeding space. However, as in an example whichwill be described later, the classification can be arranged by thecombination of three or four out of the five values including the marklength of each mark, the lengths of spaces immediately preceding andsucceeding the mark, and the mark lengths of marks with the precedingspace and succeeding space.

Next, a recording compensation method in the opticalrecording/reproduction device of the present embodiment is described.FIGS. 4( a)-(f) are diagrams generally illustrating the relationshipbetween the mark length and the waveform of the write pulse signal 1206.FIG. 4( a) shows the waveform of the reference time signal 1201 whichserves as the time reference in the recording operation. As previouslydescribed, the period of the reference time signal 1201 is Tw. FIG. 4(b) shows the count signal 1204 which is generated by a counter. Thecount signal 1204 counts the time from the leading end of the mark bythe units of reference time Tw. The timings at which the count signaltransitions to 0 correspond to the leading ends of marks or spaces.

FIGS. 4( c)-(f) show examples of the waveform of the write pulse signal1206 during the formation of record marks. The level of the write pulsesignal 1206 is modulated among three values, the peak power (Pw) whichis the highest level, the space power (Ps) which is a level forirradiation of space intervals, and the bottom power level (Pb) which isthe lowest level. After the trailing end pulse, a cooling pulse isformed at the bottom power level.

In FIGS. 4( c)-(f), the vertical axis represents the power level at thetime of laser emission, and the horizontal axis represents time.

Note that, although in this example the power level is modulated amongthree values, the cooling power level (Pc) which is taken for thecooling pulse that succeeds the trailing end pulse and the bottom powerlevel (Pb) for an intermediate pulse may have different levels, suchthat the power level can be modulated among four values in total. Thebottom power level may be between the space power level and the peakpower level although in FIG. 4 the bottom power level is lower than thespace power level. Although in the case of a write-once optical discmedium the power level for irradiation of the space intervals isreferred to as “space power”, the power level is sometimes referred toas “erase power (Pe)” because erasure of previously-recorded marks in arewritable optical disc medium by means of spaces is realized by erasingthe recorded marks using the power for the space intervals.

In FIGS. 4( c)-(f), the write pulse signal for the 4Tw mark includes oneintermediate pulse. However, as the mark length (code length) increasesby the units of 1Tw, e.g., 5Tw, 6Tw, and so on, the number ofintermediate pulses accordingly increases one by one.

A pulse which includes N−1 peak power level pulses as shown as anexample in FIG. 4 is utilized for recording of a mark with mark lengthN. Such a pulse is referred to as a so-called N−1 type write pulse.However, an N−2 type pulse, an N/2 type pulse, a so-called castle-typewrite pulse which includes an intermediate power level between the twopeak power levels, or a so-called L-type write pulse in which the secondpeak power level of the castle type is equal to the intermediate powerlevel may be utilized. As a matter of course, the description presentedbelow is applicable to these cases.

An example of the L-type write pulse is now described. FIGS. 5( a)-(f)are diagrams generally illustrating the relationship between the marklength and the waveform of the write pulse signal 1206. FIG. 5( a) showsthe waveform of the reference time signal 1201 which serves as the timereference in the recording operation. The period of the reference timesignal 1201 is Tw. FIG. 5( b) shows the count signal 1204 which isgenerated by a counter. The count signal 1204 counts the time from theleading end of the mark by the units of reference time Tw. The timingsat which the count signal transitions to 0 correspond to the leadingends of marks or spaces.

FIGS. 5( c)-(f) show examples of the waveform of the write pulse signal1206 during the formation of record marks. The level of the write pulsesignal 1206 is modulated among four values, the peak power (Pw) at thehighest level, the intermediate power (Pm) at an intermediate powerlevel, the space power (Ps) at a level for irradiation of spaceintervals, and the cooling power level (Pc) at the lowest level.

The intermediate power level may be lower than the space power levelalthough it is higher than the space power level in FIG. 5. Although inthe case of a write-once optical disc medium the power level forirradiation of the space intervals is referred to as “space power”, thepower level is sometimes referred to as “erase power (Pe)” becauseerasure of previously-recorded marks in a rewritable optical disc mediumby means of spaces is realized by erasing the recorded marks using thepower for the space intervals.

The adaptive recording compensation of the present invention uses arecording compensation table in which each mark is classified accordingto the combination of: the mark length of an interested mark for which awrite pulse train is generated; and the lengths of spaces with thepreceding interested mark and succeeding interested mark; and/or thelengths of marks immediately succeeding and preceding the spaces. And, awrite pulse signal is generated in which the position of the first orsecond pulse edge counted from an end of a write pulse train forrecording of each mark is changed according to a result of theclassification by edge change amount dTF1, dTF2 or/and dTE1, dTE2. Inthis way, the leading end position or trailing end position of a mark isprecisely controlled in the formation of the mark on the optical discmedium for recording of information. Thus, the leading end position ortrailing end position of the mark can be controlled more precisely withconsideration for optical intersymbol interference and thermalinterference as compared with a conventional classification method whereeach mark is only classified according to the length of the mark and thelength of a space with the succeeding mark in terms of the leading endedge and according to the length of the mark and the length of a spacewith the preceding mark in terms of the trailing end edge.

Specifically, the classification in the recording compensation table isarranged such that, if an interested mark has the length of 2T (shortestmark) and the length of a space with the succeeding interested mark is2T (shortest space), the interested mark is further classified accordingto the length of a mark that immediately precedes the immediatelypreceding space. And, a write pulse signal is generated in which theposition of the first, second, or third pulse edge counted from an endof a write pulse train for recording of each mark is changed accordingto a result of the classification by edge change amount dTF1, dTF2, dTF3or/and dTE1, dTE2, dTE3. This is more effective in precisely controllingthe leading end position or trailing end position of the mark in theformation of the mark on the optical disc medium for recording ofinformation.

Likewise, the classification in the recording compensation table isarranged such that, if an interested mark has the length of 2T (shortestmark) and the length of a space with the preceding mark is 2T (shortestspace), the interested mark is further classified according to thelength of a mark that immediately succeeds the space. And, a write pulsesignal is generated in which the position of the first, second, or thirdpulse edge counted from an end of a write pulse train for recording ofthe mark is changed according to a result of the classification by edgechange amount dTF1, dTF2, dTF3 or/and dTE1, dTE2, dTE3. This is moreeffective in precisely controlling the leading end position or trailingend position of the mark in the formation of the mark on the opticaldisc medium for recording of information.

As previously described, in the case where the shortest mark (2T) andthe shortest space (2T) consecutively occur, the recording compensationis made with classification by the lengths of the preceding andsucceeding marks into the classes of “shortest mark length (2T)” and“longer than 2T”, so that the number of classes for the recordingcompensation can be decreased. Also, the optical intersymbolinterference and thermal interference can effectively be removed withoutincreasing the complexity of the LSI configuration. Note that, in thecase where the shortest 2T mark and the shortest 2T space consecutivelyoccur, the recording compensation may be made with consideration for atleast one of the mark length of the mark that precedes the precedingspace and the mark length of the mark that succeeds the succeedingspace.

The recording/reproduction device of the present invention uses anoptical pickup which includes a semiconductor laser with the laserwavelength of 405 nm and an objective lens of NA=0.85 and in which thelaser power for reproduction is set to 1 mW. The disc configuration is a3-layer optical disc medium including three data recording layerscounted from the incident side of laser, on and from respective ones ofwhich information is recordable and reproducible. Therefore, in the casewhere the effective spot diameter of the laser during reproduction isthe diameter of an area equal to 1/e^2 of the peak intensity of theGaussian beam, the effective spot diameter is represented as0.82×(λ/NA), which is approximately 0.39 μm. Thus, in such an opticalsystem, record marks including the shortest marks of 0.111 μm are beyondthe optical resolution limit at which the optical spot is capable ofidentifying marks.

The reproduction signal amplitude of a signal reproduced from a recordedmark using a light beam decreases as the recorded mark becomes shorter,and reaches 0 at the optical resolution limit. The inverse of thisrecorded mark is the spatial frequency.

The relationship between the spatial frequency and the signal amplitudeis referred to as an OTF (Optical Transfer function). The signalamplitude linearly decreases as the spatial frequency increases. Thelimit at which the signal amplitude reaches 0 is referred to as OTFcutoff frequency. The OTF-spatial frequency relationship in theabove-described optical system is illustrated in FIG. 6. In the case ofthe above-described optical system, the cutoff cycle of OTF iscalculated from wavelength λ and NA of the objective lens, which isλ/NA×0.5. Specifically, when λ=405 nm and NA=0.85, the cutoff cycle is0.237 μm. The shortest mark length is a half of the cutoff cycle, i.e.,0.1185 μm. When the shortest mark length is 0.111 μm or 0.116 μm,recorded marks having a spatial frequency higher than the cutofffrequency are included, where marks can be optically reproduced up tothe cutoff frequency. Therefore, reproduction and recording aredifficult. The limit of the cutoff frequency varies due to variations inthe optical pickup, deformation of the record mark, the mark shape, etc.When considering the other conditions than the specific numerical valuesof the present embodiment (λ=405 nm, NA=0.85) under which the maximumspot size is achieved, for example, the laser wavelength of 410 nm, theobjective lens NA=0.84, and the error of 5% due to the above-describedvariations, ½ of the cutoff cycle of OTF is λ/NA×0.26=0.128 μm.Therefore, in recording of or reproduction from a mark of which theshortest mark length is approximately 0.128 μm or less, the opticalintersymbol interference is non-negligible.

FIGS. 7( a) and (b) are schematic diagrams which illustrate therelationship between the effective spot diameter of the light beam andthe physical size of the recorded marks. In FIGS. 7( a) and (b), thelight spot 501 is a spot of light converged on the disc surface of theoptical disc medium. The spot has a Gaussian beam shape with thediameter of 0.39 μm. FIGS. 7( a) and (b) also show recorded marks 502,503, 504, 505, 506, and 507 which have different lengths. FIG. 7( a)illustrates the relationship between recorded marks whose shortest marklength (2T) is 0.111 μm and spaces. FIG. 7( b) illustrates therelationship between recorded marks whose shortest mark length (2T) is0.149 μm and spaces. When applied to a BD with the diameter of 12 cm,the example of FIG. 7( a) is equivalent to the storage capacity of 33.4GB, and the example of FIG. 7( b) is equivalent to the storage capacityof 25 GB.

When the light spot passes across a 2T mark, the effective light beamspot diameter at the recording density of FIG. 7( a) (equivalent to 33.4GB) is equivalent to approximately 7T. In the case where data isreproduced from a 2T space with the succeeding 2T mark and in the casewhere the length of a mark that immediately precedes the immediatelypreceding space is 2T or 3T or longer, the left side part of the lightbeam spot overlaps the immediately preceding mark, so that areproduction signal is affected by the immediately preceding mark,resulting in occurrence of optical intersymbol interference. On theother hand, in reproduction from the same 2T mark, in the case where theimmediately preceding space has the length of 2T, the recording densityof FIG. 7( b) (equivalent to 25 GB) only leads to occurrence of opticalintersymbol interference which depends on the space lengths of theimmediately preceding and succeeding spaces. This is because theimmediately preceding mark is outside the effective light beam spotdiameter of the light spot, and therefore, the reproduction signal isnot affected by the preceding mark. Also, in reproduction from a 2Tmark, the same phenomenon occurs when the immediately succeeding spaceis a 2T space.

For the above reasons, in the case of a high density recording where theline density of record marks is equal to or beyond a certain value whichis determined according to the relationship between the light beam spotdiameter and the shortest mark length, an extended adaptive recordingcompensation where recording compensation is made according not only tothe lengths of spaces immediately preceding and succeeding an interestedmark but also to the lengths of marks immediately preceding andsucceeding the spaces (this is an extended version of a conventionaladaptive recording compensation where the pulse edges of the write pulseundergo adaptive compensation according to the mark length and the spacelength separately) is made such that not only thermal interference whichcan cause adverse effects in high density recording but also opticalintersymbol interference can be compensated for. However, in the casewhere the extended adaptive recording compensation is made according toa combination of the lengths of not only the immediately preceding andsucceeding spaces but also the preceding and succeeding marks, thenumber of classes for the recording compensation is enormous, andaccordingly, the process of calculating the recording compensationconditions takes a long period of time. Also, there are other demerits,such as a more complicated LSI configuration.

In the extended recording compensation method for optical disc mediaaccording to the present invention, extended recording compensation ismade according to the mark length of the immediately preceding or/andimmediately succeeding marks only when the mark interval which isdetermined according to the relationship between the light spot diameterand the shortest mark length is equal to or greater than a predeterminedvalue. More specifically, in the case where the shortest mark length is0.111 μm, recording compensation of an interested mark is provided onlywhen the space length of a space that immediately precedes or succeedsthe interested mark is 2T, and the recording compensation values arechanged according to whether the length of the immediately precedingor/and immediately succeeding mark is “2T” or “3T or longer”. Thisarrangement enables reduction in the number of classes for the recordingcompensation and efficient removal of optical intersymbol interference.

Some types of optical disc media entail large effects of thermalinterference due to diffusion of heat from the immediately precedingmark. In the case where the extensive recording compensation is appliedto an optical disc medium in which such thermal interference from thepreceding mark is large, the classification in the recordingcompensation table may be arranged by the lengths of the immediatelypreceding and succeeding spaces and the length of the mark that precedesthe immediately preceding space. That is, the classification is arrangedwithout consideration for the mark length of the succeeding mark,whereby the number of classes for the recording compensation can bedecreased. Therefore, the LSI can be simplified, and the thermalinterference can be efficiently removed.

When the thermal interference from the immediately preceding orsucceeding mark is small, the classification in the recordingcompensation table may be arranged by the lengths of spaces immediatelypreceding and succeeding an interested mark as well as by the marklength of the preceding or succeeding mark. For example, the leading endedge of the write pulse train may be classified according to the lengthof an interested mark and the lengths of spaces immediately precedingand succeeding the interested mark. The trailing end edge of the writepulse train may be classified according to the length of an interestedmark and the lengths of spaces immediately preceding and succeeding theinterested mark.

In that classification procedure, the classification for the spacelength of a space with the succeeding interested mark and the spacelength of a space with the preceding interested mark is arranged by thecombination of at least two classes, “shortest space length (n)” and“space length longer than the shortest space length (n+1 or longer)”,whereby thermal interference can be reduced more effectively. When thespace length of the space with the preceding or succeeding interestedmark is the shortest length (n), the interval between the interestedmark and a preceding or succeeding mark which is adjacent to theinterested mark with the space interposed therebetween decreases.Accordingly, the interested mark becomes more susceptible to heatproduced in the formation of the adjacent mark that precedes or succeedsthe interested mark. In view of such, the classification is arranged bythe combination of at least two classes, “shortest space length (n)” and“space length longer than the shortest space length (n+1 or longer)”,and different adjustment amounts are allocated to the shortest spacelength (n) and the space length longer than the shortest space length(n+1 or longer). In the case of the shortest space length (n), theadjustment is carried out such that more precise adjustment is possible,and therefore, the thermal interference can be reduced more effectively.In any classification method, the number of classes for the recordingcompensation can be reduced, so that the LSI can be simplified, and thethermal interference can be efficiently removed.

Next, an extensive recording compensation method in the opticalrecording method of the present embodiment is described with referenceto the flowchart of FIG. 8.

(a) First, record data is encoded to generate encoded data which is acombination of marks and spaces (S01). This encoded data corresponds tothe NRZI signal 1202 of (b) of FIG. 3.

(b) As for a mark, the mark is classified according to the combinationof the length of the mark, the lengths of spaces that immediatelyprecede and succeed the mark, and the lengths of marks with thepreceding space and succeeding space (S02). In (e) of FIG. 3, the 2Tmark is “X-2-2-3-3”, the 3T mark is “2-3-3-4-5”, the 5T mark is“3-4-5-2-6”, and the 6T mark is “5-2-6-2-X”. Here, X represents a codelying outside the diagram and is actually a numeric character classifiedaccording to the code sequence. The values are aligned in the order of“the length of the preceding mark”, “the length of the preceding space”,“the mark length of the interested mark in recording compensation”, “thelength of the succeeding space”, and “the length of the succeedingmark”.

(c) The position of the first or/and second pulse edge counted from anend of the write pulse train for the formation of the mark is changedaccording to the result of the classification, whereby the write pulsetrain is controlled (S03). For example, in (c) to (f) of FIG. 4, theposition of the first or/and second pulse edge counted from the leadingend is shifted by edge change amount dTF1 or/and dTF2. Further, theposition of the first or/and second pulse edge counted from the trailingend is changed by edge change amount dTE1 or/and dTE2.

(d) The optical disc medium is irradiated with the write pulse trainsuch that the mark is formed (S04).

FIGS. 9( a) to (d) are diagrams generally illustrating recording of amark 601 with the mark length of 2T under the circumstances where thepositions of the first and second pulse edges counted from the leadingend of the write pulse train are changed by edge change amounts dTF1 anddTF2. FIG. 9( a) shows the waveform of the reference time signal 1201which serves as the time reference for the recording operation. FIG. 9(b) is the count signal 1204 generated by the counter. FIG. 9( c) showsthe waveform of the write pulse signal 1206. In the write pulse signal1206, the positions of the first and second pulse edges counted from theleading end are changed by edge change amounts dTF1 and dTF2. FIG. 9( d)shows an image of the mark 601 with the mark length of 2T which isrecorded by means of the write pulse train of FIG. 9( c). The leadingend position of the mark 601 can be precisely controlled using the writepulse train.

Edge change amounts dTF1 and dTF2 are defined based on a result ofclassification into any of a plurality of predetermined classesaccording to the mark length of a mark which is to be recorded, thelengths of the preceding and succeeding spaces, and the lengths of marksthat precede and succeed the preceding and succeeding spaces, as in theclassification tables shown in FIG. 10( a) and FIG. 10( c). FIG. 10( a)shows the move amounts of dTF1, dTF2, and dTF3 of the write pulse train.For example, “M3224” in the table defines the edge movement, whichrepresents the edge move amount of the write pulse in recording of a 2Tmark under the circumstances where the length of a space with thepreceding 2T mark is 4T, the length of a space with the succeeding 2Tmark is 2T, and the length of a mark with the succeeding space is 3T orlonger. Here, as an example different from the values of the showntable, the values of dTF1, dTF2, and dTF3 may be different. FIG. 10( b)shows the move amounts of dTF1, dTF2, and dTF3 of the write pulse train.For example, “S4223” in the table defines the edge movement, whichrepresents the edge move amount of the write pulse in recording of a 2Tmark under the circumstances where the length of a space with thesucceeding 2T mark is 4T, the length of a space with the preceding 2Tmark is 2T, and the length of a mark that succeeds the succeeding spaceis 3T or longer. Here, as an example different from the values of theshown table, the values of dTF1, dTF2, and dTF3 may be different.

FIG. 10( c) shows the move amounts of dTF1, dTF2, and dTF3 of the writepulse train. For example, “M32222” in the table defines the edgemovement. Specifically, it represents the edge move amount of the writepulse in recording of a 2T mark under the circumstances where the lengthof a space with the preceding 2T mark is 2T, the length of a mark thatimmediately succeeds the succeeding space is 2T, the length of a spacewith the succeeding 2T mark is 2T, and the length of a mark thatimmediately precedes the preceding space is 3T or longer. Here, as anexample different from the values of the shown table, the values ofdTF1, dTF2, and dTF3 may be different.

FIG. 10( d) shows the move amounts of dTF1, dTF2, and dTF3 of the writepulse train. For example, “S22223” in the table defines the edgemovement. Specifically, it represents the edge move amount of the writepulse in recording of a 2T mark under the circumstances where the lengthof a space with the succeeding 2T mark is 2T, the length of a mark thatimmediately precedes the preceding space is 2T, the length of a spacewith the preceding 2T mark is 2T, and the length of a mark thatimmediately succeeds the succeeding space is 3T or longer. Here, as anexample different from the values of the shown table, the values ofdTF1, dTF2, and dTF3 may be different.

Especially in the case of FIG. 10( c) and FIG. 10( d), theclassification in the recording compensation table is arranged suchthat, if an interested mark is 2T (shortest mark) and the length of aspace immediately preceding or succeeding the interested mark is 2T(shortest space), the interested mark is classified according to whetherthe length of a mark that precedes or succeeds the immediately precedingor succeeding space is “2T” or “longer than 2T”. A write pulse signal isgenerated in which the position of the first, second, or third pulseedge counted from an end of the write pulse train for recording of eachmark is changed according to a result of the classification by edgechange amount dTF1, dTF2, dTF3 or/and dTF1, dTF2, dTF3. Using such anarrangement to precisely control the leading end position or trailingend position of a mark which is to be formed on the optical disc mediumin recording of the mark is more effective.

Also, the classification in the recording compensation table is arrangedsuch that, if an interested mark is 3T or longer (a mark other than theshortest mark), the interested mark is classified according to whether aspace with the succeeding interested mark is a 2T space (shortestspace), a 3T space, a 4T space, or a 5T or longer space. A write pulsesignal is generated in which the position of the first, second, or thirdpulse edge counted from the leading end portion of the write pulse trainfor recording of each mark is changed according to a result of theclassification by edge change amount dTF1, dTF2, dTF3. Using such anarrangement to precisely control the leading end position of a markwhich is to be formed on the optical disc medium in recording of themark is more effective.

The classification in the recording compensation table is also arrangedsuch that, if an interested mark is 3T or longer (a mark other than theshortest mark), the interested mark is classified according to whether aspace with the preceding mark is a 2T space (shortest space), a 3Tspace, a 4T space, or a 5T or longer space. A write pulse signal isgenerated in which the position of the first, second, or third pulseedge counted from the trailing end portion of the write pulse train forrecording of each mark is changed according to a result of theclassification by edge change amount dTF1, dTF2, or dTF3. Using such anarrangement to precisely control the trailing end position of a markwhich is to be formed on the optical disc medium in recording of themark is more effective.

As described above, when the shortest mark (2T) is immediately precededor succeeded by the shortest space (2T), i.e., the shortest intervals(2T) consecutively occur, the recording compensation is made withclassification by the lengths of the preceding and succeeding marks intothe classes of “shortest mark length (2T)” and “longer than 2T”.Therefore, the number of classes in the recording compensation can bedecreased. The optical intersymbol interference or thermal interferencecan efficiently be removed without increasing the complexity of the LSIconfiguration.

Edge change amounts dTF1 and dTF2 are defined by 35 classes in total.Specifically, the mark length of a mark which is to be recorded has 4classes, “2T”, “3T”, “4T”, and “5T or longer”, and the length of thepreceding space has 4 classes, “2T”, “3T”, “4T”, and “5T or longer”.Further, under the circumstance where the preceding space is a 2T space,the length of the mark that precedes the preceding space has 2 classes,“2T” and “3T or longer”. In the case of a 2T mark, the length of thesucceeding space has 4 classes, “2T”, “3T”, “4T”, and “5T or longer”.Note that, herein, as for edge shift amounts dTF1, dTF2 and dTF3, thereare 4 classes for the mark length, 4 classes for the length of thepreceding space, and 2 classes for the length of the preceding mark,although the present invention is not limited to this example. Forexample, there may be 3 classes, 5 classes, or more than 5 classes forthe mark length. There may be 2 classes, 3 classes, 5 classes, or morethan 5 classes for the length of the preceding space. There may be 3classes for the length of the preceding mark.

In a combination of mark and space lengths in the same class, edgechange amounts dTF1 and dTF2 may have equal values. In this case, thepulse length of a peak power interval of the leading end pulse is fixed.Especially when recording is carried out with a write pulse signal inwhich the number of pulses at the peak power level is one, the recordingposition of the record mark can be shifted without changing the size ofthe record mark. Thus, the edge position can be adjusted more precisely.When recording is carried out with a write pulse signal in which thenumber of pulses at the peak power level is one, edge change amountsdTF1, dTF2, and dTF3 in a combination of mark and space lengths in thesame class may have equal values where dTF3 is the edge change amountfor the third pulse edge position counted from the leading end of thewrite pulse train. In this case, the write pulse train is recorded withan anterior or posterior shift while the shape of the write pulse trainitself is kept unchanged. Further, the pulse time width of the coolingpulse can be fixed, and therefore, change in size or shift in positionof the record mark, which would occur according to the time width of thecooling pulse as especially in rewritable recording media, can beprevented. Thus, the edge position can be adjusted more precisely. Theseedge change amounts dTF1 and dTF2 may be defined by, for example, theabsolute time, such as M2222=0.5 nsec in FIG. 10( a). Alternatively,they may be defined based on the reference time signal, for example, inthe form of a value which is an integral multiple of Tw/16.Alternatively, they may be defined in the form of a value which is amultiple of Tw/32.

As for a 2T mark, a 3T mark, a 4T mark, and a 5T or longer mark, onevalue may be held as a reference value for dTF1, dTF2, dTF3, dTE1, dTE2,dTE3, and a recording compensation value which depends on the length ofthe preceding or succeeding space or the length of the preceding orsucceeding mark may be prepared as difference information for theaforementioned reference value for the respective mark lengths. Withsuch an arrangement, especially when the recording compensation whichdepends on the length of the preceding or succeeding space or recordingcompensation which depends on the length of the preceding or succeedingmark is not provided, only the reference value for the respective marklengths is read out, without reading out the difference information, sothat the recording compensation value can be read out of the disc at ahigh rate. Also, the memory of a recording device can be saved, so thatthe configuration of the LSI can be simplified. Further, by recordingthe difference information, the number of bits of a recordingcompensation value which is to be recorded in the disc can be decreased.

As described above, the position of the first or/and second or/and thirdpulse edge counted from the leading end of the write pulse signal ischanged by edge change amount dTF1, dTF2, dTF3, whereby the leading endposition of the mark can be controlled more precisely. Further, thepulse edge is controlled according not only to the mark length of a markwhich is to be recorded but also to the lengths of the preceding andsucceeding spaces. In recording of a 2T mark, when the length of thepreceding space is 2T, the pulse edge is controlled according to thelength of the preceding mark. Therefore, in the case of performing highdensity recording which is beyond the limit of OTF, the leading endposition of the mark 601 can precisely be controlled with considerationfor thermal interference or optical intersymbol interference.

FIGS. 11( a) to (d) are diagrams generally illustrating recording of amark 1401 with the mark length of 2T under the circumstances where thepositions of the first, second, and third pulse edges counted from thetrailing end of the write pulse train are changed by edge change amountsdTE1, dTE2, and dTE3, respectively. FIG. 11( a) shows the waveform ofthe reference time signal 1201 which serves as the time reference forthe recording operation. FIG. 11( b) is the count signal 1204 generatedby the counter. FIG. 11( c) shows the waveform of the write pulse signal1406. In the count signal 1204, the positions of the first, second, andthird pulse edges counted from the trailing end are changed by edgechange amounts dTF1, dTF2, and dTE3. FIG. 11( d) shows an image of themark 1401 with the mark length of 2T which is recorded by means of thewrite pulse train of FIG. 11( c). It is shown that the trailing endposition of the mark 1401 can be precisely controlled using the writepulse train.

Edge change amounts dTE1, dTE2, and dTE3 are defined based on a resultof classification made according to the mark length of a mark which isto be recorded, the lengths of the preceding and succeeding spaces, andthe lengths of marks that precede and succeed the preceding andsucceeding spaces as in the classification tables shown in FIG. 10( b)and FIG. 10( d).

As previously described in FIG. 3, the classification in the recordingcompensation table is arranged such that, if an interested mark is 2T(shortest mark) and the length of a space with the succeeding interestedmark is 2T (shortest space), the interested mark is classified accordingto the mark length of a mark that precedes the immediately precedingspace. The classification in the recording compensation table is alsoarranged such that, if an interested mark is 2T (shortest mark) and thelength of a space with the preceding interested mark is 2T (shortestspace), the interested mark is classified according to the mark lengthof a mark that succeeds the immediately succeeding space. And, a writepulse signal is generated in which the position of the edge of the writepulse train for recording of each mark is changed according to a resultof the classification by edge change amount dTF1, dTF2, dTF3 or/anddTE1, dTE2, dTE3. And, the leading end position or trailing end positionof the mark which is to be formed on the optical disc medium can beprecisely controlled in recording of data.

More specifically, the classification is as shown in FIG. 12. As fordTF1 and dTF2, in recording of a 2T mark, the lengths of spacespreceding and succeeding the 2T mark have 4 classes, “2T”, “3T”, “4T”,and “5T or longer”. Under the circumstance where the length of the spacethat precedes or succeeds the 2T mark is 2T, the length of a mark thatprecedes or succeeds the preceding or succeeding space has two classes,“2T” and “3T or longer”. That is, there are 25 classes in total (1 to25). And, each is defined by information of 1 byte. In recording of amark of 3T, 4T, or 5T or longer, the length of the preceding space has 4classes, “2T”, “3T”, “4T”, and “5T or longer”. That is, there are 12classes in total (26 to 37), and each is defined by information of 1byte.

Likewise, dTE1 is defined such that, in recording of a 2T mark, thelength of the succeeding space has 4 classes, “2T”, “3T”, “4T”, and “5Tor longer”. Under the circumstance where the length of the succeedingspace is 2T, the length of a mark that succeeds the succeeding space has2 classes, “2T” and “3T or longer”. That is, there are 10 classes intotal (1 to 10). Each is defined by information of 1 byte. In recordingof a mark of 3T, 4T, or 5T or longer, the length of the succeeding spacehas 4 classes, “2T”, “3T”, “4T”, and “5T or longer”. That is there are12 classes in total (11 to 22). And each is defined by information of 1byte.

Here, as for dTF1, dTF2, dTE1, and dTE2 of FIG. 12, in the case of anN−1 type write strategy shown in FIG. 4, dTF1 represents the informationabout the rising position of the leading end pulse, dTF2 represents theinformation about the falling position of the leading end pulse, dTE1represents the information about the rising position of the coolingpulse, and dTE2 represents the information about the falling position ofthe trailing end pulse of a 3T or longer mark. Likewise, in the case ofan L-type write strategy of FIG. 5, dTF1 represents the rising positionof the leading end pulse, dTF2 represents the falling position of theleading end pulse, dTE1 represents the rising position of the coolingpulse, and dTE2 represents the falling position of the intermediatepower of a 3T or longer mark. Although dTF2 is defined herein, forexample, pulse width TF2 between dTF1 and dTF2 may be defined instead ofdTF2. Likewise, although dTE2 is defined herein, for example, pulsewidth TE2 between dTE2 and dTE3 may be defined instead of dTE2.

In the case of small interference by the preceding and succeeding marks,the classification may be simplified as shown in FIG. 13. Specifically,as for dTF1 and dTF2, in recording of a 2T mark, the lengths of thepreceding and succeeding spaces have 4 classes, “2T”, “3T”, “4T”, and“5T or longer”, i.e., there are 4×4=16 classes (1 to 16), and each isdefined by information of 1 byte. In recording of a mark of 3T, 4T, or5T or longer, the length of the preceding space has 4 classes, “2T”,“3T”, “4T”, and “5T or longer”, i.e., there are 12 classes in total (17to 28), and each is defined by information of 1 byte.

Likewise, as for dTE1, in recording of a 2T mark, the length of thesucceeding space has 4 classes, “2T”, “3T”, “4T”, and “5T or longer”,and the length of the preceding space has 2 classes, “2T” and “3T orlonger”. That is, there are 8 classes in total (1 to 8), and each isdefined by information of 1 byte. In recording of a mark of 3T, 4T, or5T or longer, the length of the preceding space has 4 classes, “2T”,“3T”, “4T”, and “5T or longer”. That is, there are 12 classes in total(9 to 20). And each is defined by information of 1 byte. As for dTE2, inrecording of a mark of “3T”, “4T”, or “5T or longer”, the length of thepreceding space has 4 classes, “2T”, “3T”, “4T”, and “5T or longer”.That is, 12 classes in total (1 to 12), and each is defined byinformation of 1 byte.

These edge change amounts dTE1, dTE2 and dTE3 are defined with 4 classesfor the mark length of a mark which is to be recorded, “2T”, “3T”, “4T”,and “5T or longer”, 4 classes for the length of the succeeding space,“2T”, “3T”, “4T”, and “5T or longer”, and under the circumstance wherethe succeeding space is a 2T space, 2 classes for the length of a markthat succeeds the succeeding space, “2T”, “3T”, “4T”, and “5T orlonger”, and under the circumstance where it is a 2T mark, 4 classes forthe length of the preceding space, “2T”, “3T”, “4T”, and “5T or longer”,i.e., 35 classes in total. Note that, herein, as for edge shift amountsdTE1, dTE2, and dTE3, there are 4 classes for the mark length, 4 classesfor the length of the succeeding space, and 2 classes for the length ofthe succeeding mark, although the present invention is not limited tothis example. For example, there may be 3 classes, 5 classes, or morethan 5 classes for the mark length. There may be 2 classes, 3 classes, 5classes, or more than 5 classes for the length of the succeeding space.There may be 3 classes for the length of the succeeding mark. It is alsopreferable that the length of the preceding space has 2 classes, “2T”and “3T or longer”, while the length of the succeeding space also has 2classes, “2T” and “3T or longer”.

An example where the length of the succeeding space has two classes isnow described. In this case, the length of the succeeding space onlyneed to be generally categorized into the classes of “2T” or “3T orlonger”. This is clearly shown in FIG. 13 in which the “succeeding mark”(“S-mark”) has two classes, “2T” and “3T or longer”. As the value for“3T or longer” under the circumstances where “S-mark” is “2T” or “3T orlonger”, the values in the column of “3T space” of FIG. 13 can beutilized. Note that, in the descriptions of FIG. 13, the mark succeedingthe 2T mark (“S-mark”) has the mark of “X”, which means “no definition”(Don't CARE), in both columns of “2T” and “3T or longer”. However, thisis just labeling of “X” as an example. It is to be grasped that thecolumns labeled with “X” are directed to determination as to whether thespace that succeeds the 2T mark is “2T” or “3T or longer”.

In a combination of mark and space lengths in the same class, edgechange amounts dTE1, dTE2, and dTE3 may have equal values. In this case,the pulse length of a peak power interval of the leading end pulse isfixed. Especially when recording is carried out with a write pulsesignal in which the number of pulses at the peak power level is one, theposition of the record mark can be shifted without changing the size ofthe record mark. Thus, the edge position can be adjusted more precisely.

When recording is carried out with a write pulse signal in which thenumber of pulses at the peak power level is one, edge change amountsdTE2, dTE3, and dTE1 in the combination of mark and space lengths in thesame class may have equal values where dTE1 is the first pulse edgeposition counted from the trailing end of the write pulse train. In thiscase, the write pulse train is recorded with an anterior or posteriorshift while the shape of the write pulse train itself is kept unchanged.Further, the pulse time width of the cooling pulse can be fixed, andtherefore, change in size or shift in position of the record mark, whichwould occur according to the time width of the cooling pulse asespecially in rewritable recording media, can be prevented. Thus, theedge position can be adjusted more precisely.

These edge change amounts dTE2 and dTE3 may be defined by, for example,the absolute time, such as S2222=0.5 nsec in FIG. 10( b). Alternatively,they may be defined based on the reference time signal in the form of avalue which is an integral multiple of Tw/16.

As described above, the position of the second or/and third or/and firstpulse edge counted from the trailing end of the write pulse signal ischanged by edge change amount dTE2, dTE3, dTE1, whereby the trailing endposition of the mark can be controlled more precisely. Further, thepulse edge is controlled according not only to the mark length of a markwhich is to be recorded but also to the lengths of the preceding andsucceeding spaces. In recording of a 2T mark, when the length of thesucceeding space is 2T, the pulse edge is controlled according to thelength of a mark that succeeds the succeeding space. Therefore, in thecase of performing high density recording which is beyond the limit ofOTF, the trailing end position of the mark 1401 can precisely becontrolled with consideration for thermal interference or opticalintersymbol interference.

Although in the embodiment of the present invention the write pulse edgein recording of a 2T mark is controlled according to the lengths ofmarks that respectively precede and succeed the preceding and succeeding2T spaces, a write pulse edge in recording of a 3T or longer mark may beadjusted according to the lengths of marks that respectively precede andsucceed the preceding and succeeding 2T spaces. The write pulse edgeadjustment may be carried out on a 3T or longer record marksimultaneously with adjustment of a 2T mark. With such an arrangement,in the case of performing high density recording which is beyond thelimit of OTF, the leading or trailing end position of the record markcan precisely be controlled with consideration for thermal interferenceor optical intersymbol interference.

Next, a method for detecting a shift in a reproduction signal in orderto provide the extended recording compensation in the shift detectingsection 109 is described. First, an operation of Viterbi decoding basedon a PR(1,2,2,2,1)ML method in the PRML processing section 108 isdescribed.

Signal processing in a reproduction system during reproduction from ahigh density optical disc medium according to the present inventionemploys a PR(1,2,2,2,1)ML method. The recording code used herein is aRun Length Limited code, such as RLL(1,7) code. The PR(1,2,2,2,1)ML isdescribed with reference to FIG. 14 and FIG. 15. By combiningPR(1,2,2,2,1)ML with RLL(1,7), the number of possible states of thedecoding section is reduced to 10, the number of state transition pathsbecomes 16, and there are 9 reproduction levels. FIG. 14 is a statetransition diagram commonly used in the description of PRML, showingstate transition rules of PR(1,2,2,2,1)ML. Here, ten states arerepresented by identifying, at a certain point in time, a state S (0, 0,0, 0) by S0, a state S (0, 0, 0, 1) by S1, a state S (0, 0, 1, 1) by S2,a state S (0, 1, 1, 1) by S3, a state S (1, 1, 1, 1) by S4, a state S(1, 1, 1, 0) by S5, a state S (1, 1, 0, 0) by S6, a state S (1, 0, 0, 0)by S7, a state S (1, 0, 0, 1) by S8, and a state S (0, 1, 1, 0) by S9,respectively, where “0” or “1” in the parentheses represents a signalsequence on the time axis and shows what state could be produced as aresult of the next state transition from the current state. Also, thisstate transition diagram can be rearranged along the time axis into thetrellis diagram as shown in FIG. 15.

In the state transitions of PR(1,2,2,2,1)ML shown in FIG. 15, there arean infinite number of state transition patterns (i.e., combinations ofstates) that can take two state transition paths in making a transitionfrom a particular state at a certain point in time into anotherparticular state at the next point in time. If we pay attention to onlypatterns that are particularly likely to produce errors in a certaintime range, the state transition patterns of PR(1,2,2,2,1)ML may besummarized as in the following Tables 1, 2 and 3:

TABLE 1 STATE RECORDING CODE TRANSITION (b_(k i), . . . , b_(k)) k − 9 k− 8 k − 7 k − 6 k − 5 k − 4 k − 3 S0_(k−5) → S6_(k) (0, 0, 0, 0, 1, 1,1, 0, 0) S0 S1 S2 (0, 0, 0, 0, 0, 1, 1, 0, 0) S0 S0 S1 S0_(k−5) → S5_(k)(0, 0, 0, 0, 1, 1, 1, 1, 0) S0 S1 S2 (0, 0, 0, 0, 0, 1, 1, 1, 0) S0 S0S1 S0_(k−5) → S4_(k) (0, 0, 0, 0, 1, 1, 1, 1, 1) S0 S1 S2 (0, 0, 0, 0,0, 1, 1, 1, 1) S0 S0 S1 S2_(k−5) → S0_(k) (0, 0, 1, 1, 1, 0, 0, 0, 0) S2S3 S5 (0, 0, 1, 1, 0, 0, 0, 0, 0) S2 S9 S6 S2_(k−5) → S1_(k) (0, 0, 1,1, 1, 0, 0, 0, 1) S2 S3 S5 (0, 0, 1, 1, 0, 0, 0, 0, 1) S2 S9 S6 S2_(k−5)→ S2_(k) (0, 0, 1, 1, 1, 0, 0, 1, 1) S2 S3 S5 (0, 0, 1, 1, 0, 0, 0,1, 1) S2 S9 S6 S3_(k−5) → S0_(k) (0, 1, 1, 1, 1, 0, 0, 0, 0) S3 S4 S5(0, 1, 1, 1, 0, 0, 0, 0, 0) S3 S5 S6 S3_(k−5) → S1_(k) (0, 1, 1, 1, 1,0, 0, 0, 1) S3 S4 S5 (0, 1, 1, 1, 0, 0, 0, 0, 1) S3 S5 S6 S3_(k−5) →S2_(k) (0, 1, 1, 1, 1, 0, 0, 1, 1) S3 S4 S5 (0, 1, 1, 1, 0, 0, 0, 1, 1)S3 S5 S6 S7_(k−5) → S6_(k) (1, 0, 0, 0, 1, 1, 1, 0, 0) S7 S1 S2 (1, 0,0, 0, 0, 1, 1, 0, 0) S7 S0 S1 S7_(k−5) → S5_(k) (1, 0, 0, 0, 1, 1, 1, 1,0) S7 S1 S2 (1, 0, 0, 0, 0, 1, 1, 1, 0) S7 S0 S1 S7_(k−5) → S4_(k) (1,0, 0, 0, 1, 1, 1, 1, 1) S7 S1 S2 (1, 0, 0, 0, 0, 1, 1, 1, 1) S7 S0 S1S6_(k−5) → S6_(k) (1, 1, 0, 0, 1, 1, 1, 0, 0) S6 S8 S2 (1, 1, 0, 0, 0,1, 1, 0, 0) S6 S7 S1 S6_(k−5) → S5_(k) (1, 1, 0, 0, 1, 1, 1, 1, 0) S6 S8S2 (1, 1, 0, 0, 0, 1, 1, 1, 0) S6 S7 S1 S6_(k−5) → S4_(k) (1, 1, 0, 0,1, 1, 1, 1, 1) S6 S8 S2 (1, 1, 0, 0, 0, 1, 1, 1, 1) S6 S7 S1 S4_(k−5) →S0_(k) (1, 1, 1, 1, 1, 0, 0, 0, 0) S4 S4 S5 (1, 1, 1, 1, 0, 0, 0, 0, 0)S4 S5 S6 S4_(k−5) → S1_(k) (1, 1, 1, 1, 1, 0, 0, 0, 1) S4 S4 S5 (1, 1,1, 1, 0, 0, 0, 0, 1) S4 S5 S6 S4_(k−5) → S2_(k) (1, 1, 1, 1, 1, 0, 0,1, 1) S4 S4 S5 (1, 1, 1, 1, 0, 0, 0, 1, 1) S4 S5 S6 STATE PREQUALIZATION EUCLIDEAN DISTANCE TRANSITION k − 2 k − 1 k IDEAL VALUEBETWEEN PATHS S0_(k−5) → S6_(k) S3 S5 S6 1 3 5 6 5 S2 S9 S6 0 1 3 4 4 14S0_(k−5) → S5_(k) S3 S4 S5 1 3 5 7 7 S2 S3 S5 0 1 3 5 6 14 S0_(k−5) →S4_(k) S3 S4 S4 1 3 5 7 8 S2 S3 S4 0 1 3 5 7 14 S2_(k−5) → S0_(k) S6 S7S0 5 6 5 3 1 S7 S0 S0 4 4 3 1 0 14 S2_(k−5) → S1_(k) S6 S7 S1 5 6 5 3 2S7 S0 S1 4 4 3 1 1 14 S2_(k−5) → S2_(k) S6 S8 S2 5 6 5 4 4 S7 S1 S2 4 43 2 3 14 S3_(k−5) → S0_(k) S6 S7 S0 7 7 5 3 1 S7 S0 S0 6 5 3 1 0 14S3_(k−5) → S1_(k) S6 S7 S1 7 7 5 3 2 S7 S0 S1 6 5 3 1 1 14 S3_(k−5) →S2_(k) S6 S8 S2 7 7 5 4 4 S7 S1 S2 6 5 3 2 3 14 S7_(k−5) → S6_(k) S3 S5S6 2 3 5 6 5 S2 S9 S6 1 1 3 4 4 14 S7_(k−5) → S5_(k) S3 S4 S5 2 3 5 7 7S2 S3 S5 1 1 3 5 6 14 S7_(k−5) → S4_(k) S3 S4 S4 2 3 5 7 8 S2 S3 S4 1 13 5 7 14 S6_(k−5) → S6_(k) S3 S5 S6 4 4 5 6 5 S2 S9 S6 3 2 3 4 4 14S6_(k−5) → S5_(k) S3 S4 S5 4 4 5 7 7 S2 S3 S5 3 2 3 5 6 14 S6_(k−5) →S4_(k) S3 S4 S4 4 4 5 7 8 S2 S3 S4 3 2 3 5 7 14 S4_(k−5) → S0_(k) S6 S7S0 8 7 5 3 1 S7 S0 S0 7 5 3 1 0 14 S4_(k−5) → S1_(k) S6 S7 S1 8 7 5 3 2S7 S0 S1 7 5 3 1 1 14 S4_(k−5) → S2_(k) S6 S8 S2 8 7 5 4 4 S7 S1 S2 7 53 2 3 14

TABLE 2 STATE RECORDING CODE TRANSITION (b_(k i), . . . , b_(k)) k − 9 k− 8 k − 7 k − 6 k − 5 k − 4 k − 3 S0_(k−7) → S0_(k) (0, 0, 0, 0, 1, 1,0, 0, 0, 0, 0) S0 S1 S2 S9 S6 (0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0) S0 S0 S1S2 S9 S0_(k−7) → S1_(k) (0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1) S0 S1 S2 S9 S6(0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1) S0 S0 S1 S2 S9 S0_(k−7) → S2_(k) (0,0, 0, 0, 1, 1, 0, 0, 0, 1, 1) S0 S1 S2 S9 S6 (0, 0, 0, 0, 0, 1, 1, 0, 0,1, 1) S0 S0 S1 S2 S9 S2_(k−7) → S6_(k) (0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0)S2 S3 S5 S6 S8 (0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0) S2 S9 S6 S8 S2 S2_(k−7)→ S5_(k) (0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0) S2 S3 S5 S6 S8 (0, 0, 1, 1,0, 0, 1, 1, 1, 1, 0) S2 S9 S6 S8 S2 S2_(k−7) → S4_(k) (0, 0, 1, 1, 1, 0,0, 1, 1, 1, 1) S2 S3 S5 S6 S8 (0, 0, 1, 1, 0, 0, 1, 1, 1, 1, 1) S2 S9 S6S8 S2 S3_(k−7) → S6_(k) (0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0) S3 S4 S5 S6 S8(0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0) S3 S5 S6 S8 S2 S3_(k−7) → S5_(k) (0,1, 1, 1, 1, 0, 0, 1, 1, 1, 0) S3 S4 S5 S6 S8 (0, 1, 1, 1, 0, 0, 1, 1, 1,1, 0) S3 S5 S6 S8 S2 S3_(k−7) → S4_(k) (0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1)S3 S4 S5 S6 S8 (0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1) S3 S5 S6 S8 S2 S7_(k−7)→ S0_(k) (1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0) S7 S1 S2 S9 S6 (1, 0, 0, 0,0, 1, 1, 0, 0, 0, 0) S7 S0 S1 S2 S9 S7_(k−7) → S1_(k) (1, 0, 0, 0, 1, 1,0, 0, 0, 0, 1) S7 S1 S2 S9 S6 (1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1) S7 S0 S1S2 S9 S7_(k−7) → S2_(k) (1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 1) S7 S1 S2 S9 S6(1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1) S7 S0 S1 S2 S9 S6_(k−7) → S0_(k) (1,1, 0, 0, 1, 1, 0, 0, 0, 0, 0) S6 S8 S2 S9 S6 (1, 1, 0, 0, 0, 1, 1, 0, 0,0, 0) S6 S7 S1 S2 S9 S6_(k−7) → S1_(k) (1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1)S6 S8 S2 S9 S6 (1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1) S6 S7 S1 S2 S9 S6_(k−7)→ S2_(k) (1, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1) S6 S8 S2 S9 S6 (1, 1, 0, 0,0, 1, 1, 0, 0, 1, 1) S6 S7 S1 S2 S9 S4_(k−7) → S6_(k) (1, 1, 1, 1, 1, 0,0, 1, 1, 0, 0) S4 S4 S5 S6 S8 (1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0) S4 S5 S6S8 S2 S4_(k−7) → S5_(k) (1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0) S4 S4 S5 S6 S8(1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0) S4 S5 S6 S8 S2 S4_(k−7) → S4_(k) (1,1, 1, 1, 1, 0, 0, 1, 1, 1, 1) S4 S4 S5 S6 S8 (1, 1, 1, 1, 0, 0, 1, 1, 1,1, 1) S4 S5 S6 S8 S2 STATE PR EQUALIZATION EUCLIDEAN DISTANCE TRANSITIONk − 2 k − 1 k IDEAL VALUE BETWEEN PATHS S0_(k−7) → S0_(k) S7 S0 S0 1 3 44 3 1 0 S6 S7 S0 0 1 3 4 4 3 1 12 S0_(k−7) → S1_(k) S7 S0 S1 1 3 4 4 3 11 S6 S7 S1 0 1 3 4 4 3 2 12 S0_(k−7) → S2_(k) S7 S1 S2 1 3 4 4 3 2 3 S6S8 S2 0 1 3 4 4 4 4 12 S2_(k−7) → S6_(k) S2 S9 S6 5 6 5 4 4 4 4 S3 S5 S64 4 4 4 5 6 5 12 S2_(k−7) → S5_(k) S2 S3 S5 5 6 5 4 4 5 6 S3 S4 S5 4 4 44 5 7 7 12 S2_(k−7) → S4_(k) S2 S3 S4 5 6 5 4 4 5 7 S3 S4 S4 4 4 4 4 5 78 12 S3_(k−7) → S6_(k) S2 S9 S6 7 7 5 4 4 4 4 S3 S5 S6 6 5 4 4 5 6 5 12S3_(k−7) → S5_(k) S2 S3 S5 7 7 5 4 4 5 6 S3 S4 S5 6 5 4 4 5 7 7 12S3_(k−7) → S4_(k) S2 S3 S4 7 7 5 4 4 5 7 S3 S4 S4 6 5 4 4 5 7 8 12S7_(k−7) → S0_(k) S7 S0 S0 2 3 4 4 3 1 0 S6 S7 S0 1 1 3 4 4 3 1 12S7_(k−7) → S1_(k) S7 S0 S1 2 3 4 4 3 1 1 S6 S7 S1 1 1 3 4 4 3 2 12S7_(k−7) → S2_(k) S7 S1 S2 2 3 4 4 3 2 3 S6 S8 S2 1 1 3 4 4 4 4 12S6_(k−7) → S0_(k) S7 S0 S0 4 4 4 4 3 1 0 S6 S7 S0 3 2 3 4 4 3 1 12S6_(k−7) → S1_(k) S7 S0 S1 4 4 4 4 3 1 1 S6 S7 S1 3 2 3 4 4 3 2 12S6_(k−7) → S2_(k) S7 S1 S2 4 4 4 4 3 2 3 S6 S8 S2 3 2 3 4 4 4 4 12S4_(k−7) → S6_(k) S2 S9 S6 8 7 5 4 4 4 4 S3 S5 S6 7 5 4 4 5 6 5 12S4_(k−7) → S5_(k) S2 S3 S5 8 7 5 4 4 5 6 S3 S4 S5 7 5 4 4 5 7 7 12S4_(k−7) → S4_(k) S2 S3 S4 8 7 5 4 4 5 7 S3 S4 S4 7 5 4 4 5 7 8 12

TABLE 3 STATE RECORDING CODE TRANSITION (b_(k i), . . . , b_(k)) k − 9 k− 8 k − 7 k − 6 k − 5 k − 4 k − 3 k − 2 S0_(k−9) → S6_(k) (0, 0, 0, 0,1, 1, 0, 0, 1, 1, 1, 0, 0) S0 S1 S2 S9 S6 S8 S2 S3 (0, 0, 0, 0, 0, 1, 1,0, 0, 1, 1, 0, 0) S0 S0 S1 S2 S9 S6 S8 S2 S0_(k−9) → S5_(k) (0, 0, 0, 0,1, 1, 0, 0, 1, 1, 1, 1, 0) S0 S1 S2 S9 S6 S8 S2 S3 (0, 0, 0, 0, 0, 1, 1,0, 0, 1, 1, 1, 0) S0 S0 S1 S2 S9 S6 S8 S2 S0_(k−9) → S4_(k) (0, 0, 0, 0,1, 1, 0, 0, 1, 1, 1, 1, 1) S0 S1 S2 S9 S6 S8 S2 S3 (0, 0, 0, 0, 0, 1, 1,0, 0, 1, 1, 1, 1) S0 S0 S1 S2 S9 S6 S8 S2 S2_(k−7) → S0_(k) (0, 0, 1, 1,1, 0, 0, 1, 1, 0, 0, 0, 0) S2 S3 S5 S6 S8 S2 S9 S6 (0, 0, 1, 1, 0, 0, 1,1, 0, 0, 0, 0, 0) S2 S9 S6 S8 S2 S9 S6 S7 S2_(k−7) → S1_(k) (0, 0, 1, 1,1, 0, 0, 1, 1, 0, 0, 0, 1) S2 S3 S5 S6 S8 S2 S9 S6 (0, 0, 1, 1, 0, 0, 1,1, 0, 0, 0, 0, 1) S2 S9 S6 S8 S2 S9 S6 S7 S2_(k−7) → S2_(k) (0, 0, 1, 1,1, 0, 0, 1, 1, 0, 0, 1, 1) S2 S3 S5 S6 S8 S2 S9 S6 (0, 0, 1, 1, 0, 0, 1,1, 0, 0, 0, 1, 1) S2 S9 S6 S8 S2 S9 S6 S7 S3_(k−5) → S0_(k) (0, 1, 1, 1,1, 0, 0, 1, 1, 0, 0, 0, 0) S3 S4 S5 S6 S8 S2 S9 S6 (0, 1, 1, 1, 0, 0, 1,1, 0, 0, 0, 0, 0) S3 S5 S6 S8 S2 S9 S6 S7 S3_(k−5) → S1_(k) (0, 1, 1, 1,1, 0, 0, 1, 1, 0, 0, 0, 1) S3 S4 S5 S6 S8 S2 S9 S6 (0, 1, 1, 1, 0, 0, 1,1, 0, 0, 0, 0, 1) S3 S5 S6 S8 S2 S9 S6 S7 S3_(k−5) → S2_(k) (0, 1, 1, 1,1, 0, 0, 1, 1, 0, 0, 1, 1) S3 S4 S5 S6 S8 S2 S9 S6 (0, 1, 1, 1, 0, 0, 1,1, 0, 0, 0, 1, 1) S3 S5 S6 S8 S2 S9 S6 S7 S7_(k−5) → S6_(k) (1, 0, 0, 0,1, 1, 0, 0, 1, 1, 1, 0, 0) S7 S1 S2 S9 S6 S8 S2 S3 (1, 0, 0, 0, 0, 1, 1,0, 0, 1, 1, 0, 0) S7 S0 S1 S2 S9 S6 S8 S2 S7_(k−5) → S5_(k) (1, 0, 0, 0,1, 1, 0, 0, 1, 1, 1, 1, 0) S7 S1 S2 S9 S6 S8 S2 S3 (1, 0, 0, 0, 0, 1, 1,0, 0, 1, 1, 1, 0) S7 S0 S1 S2 S9 S6 S8 S2 S7_(k−5) → S4_(k) (1, 0, 0, 0,1, 1, 0, 0, 1, 1, 1, 1, 1) S7 S1 S2 S9 S6 S8 S2 S3 (1, 0, 0, 0, 0, 1, 1,0, 0, 1, 1, 1, 1) S7 S0 S1 S2 S9 S6 S8 S2 S6_(k−5) → S6_(k) (1, 1, 0, 0,1, 1, 0, 0, 1, 1, 1, 0, 0) S6 S8 S2 S9 S6 S8 S2 S3 (1, 1, 0, 0, 0, 1, 1,0, 0, 1, 1, 0, 0) S6 S7 S1 S2 S9 S6 S8 S2 S6_(k−5) → S5_(k) (1, 1, 0, 0,1, 1, 0, 0, 1, 1, 1, 1, 0) S6 S8 S2 S9 S6 S8 S2 S3 (1, 1, 0, 0, 0, 1, 1,0, 0, 1, 1, 1, 0 S6 S7 S1 S2 S9 S6 S8 S2 S6_(k−5) → S4_(k) (1, 1, 0, 0,1, 1, 0, 0, 1, 1, 1, 1, 1) S6 S8 S2 S9 S6 S8 S2 S3 (1, 1, 0, 0, 0, 1, 1,0, 0, 1, 1, 1, 1) S6 S7 S1 S2 S9 S6 S8 S2 S4_(k−5) → S0_(k) (1, 1, 1, 1,1, 0, 0, 1, 1, 0, 0, 0, 0) S4 S4 S5 S6 S8 S2 S9 S6 (1, 1, 1, 1, 0, 0, 1,1, 0, 0, 0, 0, 0) S4 S5 S6 S8 S2 S9 S6 S7 S4_(k−5) → S1_(k) (1, 1, 1, 1,1, 0, 0, 1, 1, 0, 0, 0, 1) S4 S4 S5 S6 S8 S2 S9 S6 (1, 1, 1, 1, 0, 0, 1,1, 0, 0, 0, 0, 1) S4 S5 S6 S8 S2 S9 S6 S7 S4_(k−5) → S2_(k) (1, 1, 1, 1,1, 0, 0, 1, 1, 0, 0, 1, 1) S4 S4 S5 S6 S8 S2 S9 S6 (1, 1, 1, 1, 0, 0, 1,1, 0, 0, 0, 1, 1) S4 S5 S6 S8 S2 S9 S6 S7 STATE PR EQUALIZATIONEUCLIDEAN DISTANCE TRANSITION k − 1 k IDEAL VALUE BETWEEN PATHS S0_(k−9)→ S6_(k) S5 S6 1 3 4 4 4 4 5 6 5 S9 S6 0 1 3 4 4 4 4 4 4 12 S0_(k−9) →S5_(k) S4 S5 1 3 4 4 4 4 5 7 7 S3 S5 0 1 3 4 4 4 4 5 6 12 S0_(k−9) →S4_(k) S4 S4 1 3 4 4 4 4 5 7 8 S3 S4 0 1 3 4 4 4 4 5 7 12 S2_(k−7) →S0_(k) S7 S0 5 6 5 4 4 4 4 3 1 S0 S0 4 4 4 4 4 4 3 1 0 12 S2_(k−7) →S1_(k) S7 S1 5 6 5 4 4 4 4 3 2 S0 S1 4 4 4 4 4 4 3 1 1 12 S2_(k−7) →S2_(k) S8 S2 5 6 5 4 4 4 4 4 4 S1 S2 4 4 4 4 4 4 3 2 3 12 S3_(k−5) →S0_(k) S7 S0 7 7 5 4 4 4 4 3 1 S0 S0 6 5 4 4 4 4 3 1 0 12 S3_(k−5) →S1_(k) S7 S1 7 7 5 4 4 4 4 3 2 S0 S1 6 5 4 4 4 4 3 1 1 12 S3_(k−5) →S2_(k) S8 S2 7 7 5 4 4 4 4 4 4 S1 S2 6 5 4 4 4 4 3 2 3 12 S7_(k−5) →S6_(k) S5 S6 2 3 4 4 4 4 5 6 5 S9 S6 1 1 3 4 4 4 4 4 4 12 S7_(k−5) →S5_(k) S4 S5 2 3 4 4 4 4 5 7 7 S3 S5 1 1 3 4 4 4 4 5 6 12 S7_(k−5) →S4_(k) S4 S4 2 3 4 4 4 4 5 7 8 S3 S4 1 1 3 4 4 4 4 5 7 12 S6_(k−5) →S6_(k) S5 S6 4 4 4 4 4 4 5 6 5 S9 S6 3 2 3 4 4 4 4 4 4 12 S6_(k−5) →S5_(k) S4 S5 4 4 4 4 4 4 5 7 7 S3 S5 3 2 3 4 4 4 4 5 6 12 S6_(k−5) →S4_(k) S4 S4 4 4 4 4 4 4 5 7 8 S3 S4 3 2 3 4 4 4 4 5 7 12 S4_(k−5) →S0_(k) S7 S0 8 7 5 4 4 4 4 3 1 S0 S0 7 5 4 4 4 4 3 1 0 12 S4_(k−5) →S1_(k) S7 S1 8 7 5 4 4 4 4 3 2 S0 S1 7 5 4 4 4 4 3 1 1 12 S4_(k−5) →S2_(k) S8 S2 8 7 5 4 4 4 4 4 4 S1 S2 7 5 4 4 4 4 3 2 3 12

Table 1, Table 2, and Table 3 each show the paths of state transitionfrom their start state through their merging state, two recordingsequences that could have gone through those state transitions, twoideal waveforms that could have gone through those state transitions,and the Euclidean distance between the two ideal reproduction waveforms.

Table 1 shows 18 different pairs of state transition patterns, each ofwhich can take two different paths and has a Euclidean distance of 14between themselves. These patterns correspond to edge portions of arecord mark in the context of a reproduction waveform of an optical discmedium. In other words, these patterns represent one-bit error patternsbetween record marks and spaces. As an example, a transition pathleading from S0(k−5) to S6(k) according to the state transition rulesshown in FIG. 15 is described. In that case, one path is a case wherethe recording sequence transitions to “0, 0, 0, 0, 1, 1, 1, 0, 0” and isdetected. In the context of the recorded state where zeros (0) and ones(1) of the reproduced data are respectively replaced with spaces andmarks, this recording sequence is the sequence of a space with a lengthof 4T or longer, a 3T mark, and a space with a length of 2T or longer.This is shown as Path A waveform in FIG. 16. FIG. 16 shows two waveformswhich are different in the relationship between the sampling time andthe reproduction level. In FIG. 16, the abscissa represents the samplingtime which indicates every one cycle in the recording sequence, and theordinate represents the reproduction level. As previously mentioned,PR(1,2,2,2,1)ML has nine ideal reproduction levels in total, from Level0 through Level 8.

On the other hand, the other path is a case where the recording sequencetransitions to “0, 0, 0, 0, 0, 1, 1, 0, 0” and is detected. In thecontext of the recorded state where zeros (0) and ones (1) of thereproduced data are respectively replaced with spaces and marks, thisrecording sequence is the sequence of a space with a length of 5T orlonger, a 2T mark, and a space with a length of 2T or longer. This pathis shown as Path B waveform in FIG. 16. The patterns with a Euclideandistance of 14 shown in Table 1 are characterized by always including asingle piece of edge information which is indicative of a mark-spaceboundary. An edge adjustment method optimum for the PRML method whichtakes advantage of this feature is as described in Patent Document No.3, for example.

Likewise, Table 2 shows 18 different pairs of state transition patterns,each of which can take two different paths and has a Euclidean distanceof 12 between themselves. These patterns are patterns in which, amongshift errors of a 2T mark or a 2T space, a 2-bit error is detected. Asan example, a state transition path leading from S0(k−7) to S0(k)according to the state transition rules shown in FIG. 15 is described.In that case, one path is a case where the recording sequencetransitions to “0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0” and is detected. In thecontext of the recorded state where zeros (0) and ones (1) of thereproduced data are respectively replaced with spaces and marks, thisrecording sequence is the sequence of a space with a length of 4T orlonger, a 2T mark, and a space with a length of 5T or longer. This isshown as Path A waveform in FIG. 17.

On the other hand, the other path is a case where the recording sequencetransitions to “0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0” and is detected. In thecontext of the recorded state where zeros (0) and ones (1) of thereproduced data are respectively replaced with spaces and marks, thisrecording sequence is the sequence of a space with a length of 5T orlonger, a 2T mark, and a space with a length of 4T or longer. This isshown as Path B waveform in FIG. 17. The patterns with a Euclideandistance of 12 shown in Table 2 are characterized by always includingtwo pieces of rising and falling edge information of a 2T mark or 2Tspace.

Likewise, Table 3 shows 18 different pairs of state transition patterns,each of which can take two different paths and has a Euclidean distanceof 12 between themselves. These patterns are patterns in which a 3-biterror is detected in a portion where at least two 2T intervalsconsecutively occur, such as “2T mark-2T space” or “2T space-2T mark”.As an example, a state transition path leading from S0(k−9) to S6(k)according to the state transition rules shown in FIG. 15 is described.In that case, one path is a case where the recording sequencetransitions to “0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0” and is detected.In the context of the recorded state where zeros (0) and ones (1) of thereproduced data are respectively replaced with spaces and marks, thisrecording sequence is the sequence of a space with a length of 4T orlonger, a 2T mark, a 2T space, a 3T mark, and a space with a length of2T or longer. This is shown as Path A waveform in FIG. 18.

On the other hand, the other path is a case where the record codesequence transitions to “0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0” and isdetected. In the context of the recorded state where zeros (0) and ones(1) of the reproduced data are respectively replaced with spaces andmarks, this recording sequence is the sequence of a space with a lengthof 5T or longer, a 2T mark, a 2T space, a 2T mark and a space with alength of 2T or longer. This is shown as Path B waveform in FIG. 18. Thepatterns with a Euclidean distance of 12 shown in Table 3 arecharacterized in that a 3-bit error is detected in a portion where atleast two 2T intervals consecutively occur, such as “2T mark-2T space”or “2T space-2T mark”.

In adjustment of the position of the leading end edge or trailing endedge of a record mark, the direction and magnitude of edge deviationneed to be detected for each one of the combinations of respective marksand respective spaces. When the PR(1,2,2,2,1)ML method is used, theadjustment can be carried out using the patterns with a Euclideandistance of 14 shown in Table 1. This means that recording compensationcan be realized by adjusting the pulse edges of the write pulse trainaccording to the length of a subject mark and the lengths of itspreceding and succeeding spaces. FIG. 19 is a classification table for arecording compensation which is made using the patterns with a Euclideandistance of 14.

In the case of the patterns having a Euclidean distance of 14, therecording compensation includes 4 classes of the subject mark, “2T”,“3T”, “4T”, and “5T or longer”. Further, the length of the precedingspace has 4 classes, “2T”, “3T”, “4T”, and “5T or longer”. Thus, thereare 4×4=16 classes in total for adjustment. In this case, the writepulse train subjected to the recording compensation includes dTF1 anddTF2 of FIG. 4.

For adjustment, the mark length of the subject mark has 4 classes, “2T”,“3T”, “4T”, and “5T or longer”, and the space length of a spacesucceeding the subject mark has 4 classes, “2T”, “3T”, “4T”, and “5T orlonger”, i.e., there are 4×4=16 classes in total. In this case, thewrite pulse train subjected to the recording compensation includes dTE2,dTE3 of FIG. 4. The recording compensation is made on dTF1, dTF2, dTE2,and dTE3 according to the length of the subject mark and the lengths ofits preceding and succeeding spaces, whereby the recording compensationof the Euclidean distance of 14 is provided.

A shift detection method in the recording compensation is described. Forexample, in FIG. 16, a cumulative value of squares of the differencebetween the value of the reproduction signal from y_k−4 to y_k in theperiod from time k−4 to time k and the expected value of Path A isreferred to as Pa. Pa is expressed by Formula 1. A cumulative value ofsquares of the difference between the value of the reproduction signalfrom y_k−4 to y_k in the period from time k−4 to time k and the expectedvalue of Path B is referred to as Pb. Pb is expressed by Formula 2.Pa=(y _(—) k−4−1)^2+(y _(—) k−3−3)^2+(y _(—) k−2−5)^2+(y _(—)k−1−6)^2+(y _(—) k−5)^2  (Formula 1)Pb=(y _(—) k−4−0)^2+(y _(—) k−3−1)^2+(y _(—) k−2−3)^2+(y _(—)k−1−4)^2+(y _(—) k−4)^2  (Formula 2)

Now, the meaning of difference Pa−Pb between Pa and Pb, which isindicative of the reliability of a maximum likelihood decoding result,is described. It can be said that if Pa<<Pb the maximum likelihooddecoding section has selected Path A with confidence and that if Pa>>Pbthe maximum likelihood decoding section has selected Path B withconfidence. If Pa=Pb, the path selected by the maximum likelihooddecoding section may be any of Path A and Path B, i.e., it isfifty-fifty whether the decoding result is correct. By calculating Pa−Pbfrom a predetermined time, a predetermined number of chances, and thedecoding result in this way, the distribution of Pa−Pb is obtained.

Tracks written under the above-described write pulse conditions areconsecutively subjected to reproduction, and the edge positioninformation of the reproduced signal is measured. The light emittingsection 102 operates to perform reproduction on a track of write pulseconditions established for writing. The reproduced write pulseconditions are transmitted through the waveform equalizing section 105and the A/D conversion section 106. The PLL section 107 generates areproduction clock. A pattern detecting section included in the PRMLprocessing section 108 performs Viterbi decoding (maximum likelihooddecoding) on a digital signal sampled with the reproduction clock andgenerates a binary signal which is indicative of a result of the maximumlikelihood decoding for each set of recording conditions.

Next, a method for detecting an edge shift in the reproduction signalwhose waveform is reshaped so as to comply with PR(1,2,2,2,1)equalization is described.

FIG. 20 shows sampled values of the patterns of state transition S0→S6of Table 1 as an example of the PR equalization ideal waveform. Theabscissa represents time (1 scale period represents 1 channel clockperiod), and the ordinate represents the signal level (0 to 8). Thebroken lines and the solid lines correspond to Path A and Path B,respectively. Each of the sampled values corresponds to any of 0 to 8 ofexpected value Levelv of the input in the maximum likelihood decoding.It is defined that the waveform reproduced from a record mark portion isan upwardly-oriented waveform in terms of the signal level, and that thewaveform reproduced from a non-record portion is a downwardly-orientedwaveform. The patterns shown in FIG. 20 correspond to the reproducedwaveforms at the mark-space boundaries (the leading end edge and thetrailing end edge of the mark). Thus, the patterns of FIG. 20 and thefollowing patterns of Table 1, S0→S6, S0→S5, S0→S4, S7→S6, S7→S5, S7→S4,S6→S6, S6→S5, and S6→S4, correspond to the leading end edge portion ofthe mark, and the other patterns of Table 1, S2→S0, S2→S1, S2→S2, S3→S0,S3→S1, S3→S2, S4→S0, S4→S1, and S4→S2, correspond to the trailing endedge portion of the mark.

The reproduced waveforms of FIGS. 20( a) and 20(b) are the waveforms ofthe sequence of a 4T space and a 3T mark which are recorded in thisembodiment. Now, a method for detecting a leading end edge shift of themark is described with attention to the reproduced waveforms of FIGS.20( a) and 20(b).

FIGS. 20( a) and 20(b) show the correlation between the reproducedwaveforms for S0→S6 of Table 1 and the deviation of the record mark. InFIGS. 20( a) and 20(b), the solid line with open triangles (Δ)represents the input signal, and Path A represented by the broken lineis a correct state transition path. The input signal is generated basedon record mark A− in FIG. 20( a) and based on record mark A+ in FIG. 20(b). It is assumed that record mark A has an ideal leading end edge.

FIG. 20( a) shows the reproduced waveforms where the leading end edgeposition of the record mark is deviated to the shorter side relative tothe ideal leading end edge position. Distance Pa between Path A and theinput signal and distance Pb between Path B and the input signal arecalculated to obtain 4S3M-A=ΔA−=|Pa−Pb|−Pstd. 4S3M-A means the edgeshift between the 4T space and the 3T mark in Path A and represents theedge shift amount between the 4T space and the immediately succeeding 3Tmark. Here, as for Pstd, the value of Pa−Pb when Pa=0 is represented by−Pstd, and the value of Pa−Pb when Pb=0 is represented by Pstd.

FIG. 20( b) shows the reproduced waveforms where the leading end edgeposition of the record mark is deviated to the longer side relative tothe ideal leading end edge position. Distance Pa between Path A and theinput signal and distance Pb between Path B and the input signal arecalculated to obtain 4S3M-A=ΔA+=|Pa−Pb|−Pstd. 4S3M-A means the edgeshift between the 4T space and the 3T mark in Path A and represents theedge shift amount between the 4T space and the immediately succeeding 3Tmark.

The above-described edge shift detection is carried out on the 18patterns in total classified in Table 1 to detect the edge shift amountthat depends on the mark and space lengths.

Here, the classification of the edge shift in the patterns of Table 1which is made separately by the mark length and the space length isrealized by detecting b_k−4 bits out of 9 bits of the record code (b_k−8to b_k) as the boundary of the edge deviation between the mark and thespace or between the space and the mark. For example, in S0→S6 pattern,it corresponds to comparison subject patterns of the sequence of “4T orlonger space and 3T mark” and the sequence of “5T or longer space and 2Tmark”. The edge shift amount which depends on these mark lengths and thelengths of the preceding spaces is detected. Likewise, in S2→S0 pattern,it corresponds to comparison subject patterns of the sequence of “3Tmark and 4T or longer space” and the sequence of “2T mark and 5T orlonger space”. The edge shift amount which depends on these mark lengthsand the lengths of succeeding spaces is detected.

Next, a method for detecting the phase shift amount for the patterns ofTable 2 in which the Euclidean distance of the state transition patternsthat can take two state transition paths is 12 and in which, among shifterrors of a 2T mark or a 2T space, a 2-bit error is detected isdescribed.

FIGS. 21( a) and 21(b) show sampled values of the patterns which are tobe subjected to comparison. The abscissa represents time (1 scale periodrepresents 1 channel clock period), and the ordinate represents thesignal level (0 to 8). The broken lines and the solid lines correspondto Path A and Path B, respectively. Each of the sampled valuescorresponds to any of 0 to 8 of expected value Level v of the input inthe maximum likelihood decoding. It is defined that the waveformreproduced from a record mark portion is an upwardly-oriented waveformin terms of the signal level, and that the waveform reproduced from anon-record portion is a downwardly-oriented waveform. The patterns shownin FIGS. 21( a) and 21(b) correspond to the reproduced waveforms of thepatterns including at least one 2T mark or 2T space. Thus, in thepatterns of FIGS. 21( a) and 21(b) and the following patterns of Table2, S0→S0, S0→S1, S0→S2, S7→S0, S7→S1, S7→S2, S6→S0, S6→S1, and S6→S2,the position of the 2T mark makes an anterior or posterior shift whilekeeping its length of 2T unchanged. The other patterns of Table 2,S2→S6, S2→S5, S2→S4, S3→S6, S3→S5, S3→S4, S4→S6, S4→S5, and S4→S4,correspond to a portion where the position of the 2T space makes ananterior or posterior shift while keeping its length of 2T unchanged.

The waveforms of the sequence of a 4T or longer space, a 2T mark, and a5T or longer space recorded in the present embodiment are the reproducedwaveforms of FIGS. 21( a) and 21(b). A method for detecting a shift inthe recording position of the 2T mark is now described with attention tothe reproduced waveforms of FIGS. 21( a) and 21(b). FIGS. 21( a) and21(b) show the correlation between the reproduced waveforms for S0→S0 ofTable 2 and the deviation of the record mark. In FIGS. 21( a) and 21(b),the solid line with open triangles (Δ) represents the input signal, andPath A represented by the broken line is a correct state transitionpath. The input signal is generated based on record mark B− in FIG. 21(a) and based on record mark B+ in FIG. 21( b). It is assumed that recordmark B has an ideal recording position.

FIG. 21( a) shows the reproduced waveforms where the recording positionof the record mark (2T) is deviated to the posterior side relative tothe ideal position. Distance Pa between Path A and the input signal anddistance Pb between Path B and the input signal are calculated to obtain4S2M5S-A=ΔB−=|Pa−Pb|−Pstd. 4S2M5S-A means the recording position shiftof 2T in the sequence of a 4T or longer space, a 2T mark, and a 5T orlonger mark in Path A and represents the recording position deviationamount of the 2T mark interposed between the 4T or longer space and the5T or longer space. Here, as for Pstd, the value of Pa−Pb when Pa=0 isrepresented by −Pstd, and the value of Pa−Pb when Pb=0 is represented byPstd.

FIG. 21( b) shows the reproduced waveforms where the recording positionof the record mark (2T) is deviated to the anterior side relative to theideal position. Distance Pa between Path A and the input signal anddistance Pb between Path B and the input signal are calculated to obtain4S2M5S-A=ΔB+=|Pa−Pb|−Pstd. 4S2M5S-A means the recording position shiftof 2T in the sequence of a 4T or longer space, a 2T mark, and a 5T orlonger mark in Path A and represents the recording position deviationamount of the 2T mark interposed between the 4T or longer space and the5T or longer space. The above-described phase shift detection is carriedout on the 18 patterns in total classified in Table 2 to detect thephase shift amount that depends on the lengths of X space, 2T mark, andY space or the lengths of X′ mark, 2T space, and Y′ mark.

Here, the classification of the recording position shift of “X space, 2Tmark, Y space” or “X′ mark, 2T space, Y′ mark” in the patterns of Table2 is realized by detecting b_k−5 bits out of 11 bits of the record code(b_k−10 to b_k) as the boundary of the recording position deviation ofthe 2T mark or the 2T space. For example, in S0→S0 pattern, itcorresponds to comparison subject patterns of the sequence of “4T orlonger space, 2T mark, 5T or longer space” and the sequence of “5T orlonger space, 2T mark, 4T or longer space”. The phase shift amount whichdepends on the 2T mark length and the lengths of the preceding andsucceeding spaces is detected. Likewise, in S3→S4 pattern, itcorresponds to comparison subject patterns of the sequence of “4T mark,2T space, 4T or longer mark” and the sequence of “3T mark, 2T space, 5Tor longer mark”. The recording position shift amount which depends onthe 2T space length and the lengths of the preceding and succeedingspaces is detected.

Next, patterns in which the Euclidean distance of the state transitionpatterns that can take two state transition paths is 12 and in which a3-bit error is detected in a portion where at least two 2T intervalsconsecutively occur, such as “2T mark-2T space” or “2T space-2T mark”,are described. More specifically, a method for detecting the phase shiftamount in the patterns of Table 3 in which, among shift errors of theconsecutive sequence of “2T mark-2T space” or the consecutive sequenceof “2T space-2T mark”, a 3-bit error is detected is described.

FIG. 22 shows sampled values of the patterns which are to be subjectedto comparison. The abscissa represents time (1 scale period represents 1channel clock period), and the ordinate represents the signal level (0to 8). The broken lines and the solid lines correspond to the respectivewaveforms of Path A and Path B. Each of the sampled values correspondsto any of 0 to 8 of expected value Levelv of the input in the maximumlikelihood decoding. It is defined that the waveform reproduced from arecord mark portion is an upwardly-oriented waveform in terms of thesignal level, and that the waveform reproduced from a non-record portionis a downwardly-oriented waveform.

The patterns shown in FIG. 22 correspond to the reproduced waveformswhich have patterns including the consecutive sequence of “2T mark-2Tspace”. Thus, the patterns of FIG. 22 and the following patterns ofTable 3, S0→S6, S0→S5, S0→S4, S7→S6, S7→S5, S7→S4, S6→S6, S6→S5, andS6→S4, correspond to a portion where the position of the consecutivesequence of “2T mark-2T space” makes an anterior or posterior shift, andthe other patterns of Table 3, S2→S0, S2→S1, S2→S2, S3→S0, S3→S1, S3→S2,S4→S0, S4→S1, and S4→S2, correspond to a portion where the position ofthe consecutive sequence of “2T space-2T mark” makes an anterior orposterior shift.

The waveforms of the sequence of a 4T or longer space, a 2T mark, a 2Tspace, and a 3T mark recorded in the present embodiment are thereproduced waveforms of FIG. 22. Therefore, a method for detecting ashift in the recording position of the consecutive sequence of “2Tmark-2T space” is now described with attention to the reproducedwaveforms of FIG. 22. FIG. 22 shows the correlation between thereproduced waveforms for S0→S6 of Table 3 and the deviation of therecord mark. In FIG. 22, the solid line with open triangles (Δ)represents the input signal, and Path A represented by the broken lineis a correct state transition path. The input signal is generated basedon record mark C− in FIG. 22( a) and based on record mark C+ in FIG. 22(b). It is assumed that record mark C has an ideal recording position.

FIG. 22( a) shows a case where the recording position of the consecutivesequence of “2T mark-2T space” is deviated to the posterior siderelative to the ideal position. Distance Pa between Path A and the inputsignal and distance Pb between Path B and the input signal arecalculated to obtain 4S2M2S3M-A=ΔC−|Pa−Pb|−Pstd. 4S2M2S3M−A means therecording position shift of “2T mark-2T space” in the sequence of a 4Tor longer space, a 2T mark, a 2T space, and a 3T mark in Path A andrepresents the recording position deviation amount of “2T mark-2T space”interposed between the 4T or longer space and the 3T mark. Here, as forPstd, the value of Pa−Pb when Pa=0 is represented by −Pstd, and thevalue of Pa−Pb when Pb=0 is represented by Pstd.

FIG. 22( b) shows a case where the recording position of the consecutivesequence of “2T space-2T mark” is deviated to the anterior side relativeto the ideal position. Distance Pa between Path A and the input signaland distance Pb between Path B and the input signal are calculated toobtain 4S2M2S3M-A=ΔC+=|Pa−Pb|−Pstd. 4S2M2S3M-A means the recordingposition shift of “2T space-2T mark” in the sequence of a 4T or longerspace, a 2T mark, a 2T space, and a 3T mark in Path A and represents therecording position deviation amount of “2T space-2T mark” interposedbetween the 4T or longer space and the 3T mark.

The above-described shift detection is carried out on the 18 patterns intotal classified in Table 3 to detect the phase shift amount thatdepends on the lengths of X space, 2T mark, 2T space, and Y mark or thelengths of X′ mark, 2T space, 2T mark, and Y′ space.

Here, the classification of the recording position shift of “X space, 2Tmark, 2T space, Y mark” or “X′ mark, 2T space, 2T mark, Y′ space” in thepatterns of Table 3 is realized by detecting b_k−6 bits out of 13 bitsof the record code (b_k−12 to b_k) as the boundary of the recordingposition deviation of “2T mark-2T space” or “2T space-2T mark”. Forexample, in S0→S6 pattern, it corresponds to comparison subject patternsof the sequence of “4T or longer space, 2T mark, 2T space, a mark” andthe sequence of “5T or longer space, 2T mark, 2T space, 2T mark”. Theshift amount which depends on the lengths of these 2T mark and 2T spaceand the length of the preceding space and the length of the succeedingmark is detected. Likewise, in S2→S0 pattern, it corresponds tocomparison subject patterns of “3T mark, 2T space, 2T mark, 4T or longerspace” and “2T mark, 2T space, 2T mark, 5T or longer space”. Therecording position shift amount which depends on these 2T space and 2Tmark and the length of the preceding mark and the length of thesucceeding space is detected.

The shift detection method includes measuring |Pa−Pb|−Pstd obtained bycomparison of the Viterbi decoding and the reproduction signal for eachpattern to detect the shift amount. Based on the result of thedetection, they are converted to the respective table values for theextended recording compensation, and the recording compensation is madewith these values. However, there is another example of the shiftdetection method. For example, a portion including a bit error isextracted, and the error pattern and a code sequence of an originalrecord are compared. Based on the shift tendency of the bit error, theextended recording compensation is made. FIG. 23 shows a result ofcomparison of a correct code sequence and decoded error data based oncomparison of a correct pattern of an actually-recorded code sequenceand a Viterbi decoded bit derived from the reproduction signal. Theresult of FIG. 23 is an example result obtained by comparing, with acorrect pattern, an error portion of Viterbi-decoded data reproducedfrom a record mark which has been recorded with recording compensationbeing made according to the length of the mark and the lengths of itspreceding and succeeding spaces, i.e., only recording compensation ofmarks and spaces with the Euclidean distance of 14 in Table 1 beingmade, before the extended recording compensation.

In FIG. 23, each pair of bars includes a data sequence of a correctpattern, i.e., a data sequence of an original record, on the left. Shownon the right is a result of an error in reproduced data obtained byViterbi decoding a signal reproduced from part of an optical disc mediumin which a correct pattern is recorded. In each bar, represents a markof 1T, and “1” represents a space of 1T. For example, “00” represents a2T mark, and “000” represents a 3T mark. Among the pairs of codesequences shown in FIGS. 23( a) and 23(b), FIG. 23( a) shows acollection of code sequences erroneously detected as having made ananterior shift relative to the correct code sequences, and FIG. 23( b)shows a collection of code sequences erroneously detected as having madea posterior shift relative to the correct code sequences. Recording andreproduction of the code sequences advance from top to bottom of thedrawing.

The leftmost pair of code sequences in FIG. 23( a) is part of a codesequence in which an error actually occurred in recording of the codesequence of “4T space, 2T mark, 2T space, 3T space” and which waserroneously detected as being “3T space, 2T mark, 2T space, 3T mark”.The error recognized herein is such that each of “2T mark, 2T space, 3Tmark” has made an anterior shift by 1 bit. The leftmost pair of codesequences in FIG. 23( b) is part of a code sequence in which an erroractually occurred in recording of the code sequence of “3T mark, 2Tspace, 2T mark, 3T space” and which was erroneously detected as being“4T space, 2T mark, 2T space, 3T mark”. The error recognized herein issuch that each of “3T mark, 2T space, 2T mark” has made a posteriorshift by 1 bit.

Checking all the pairs of error code sequences of FIGS. 23( a) and23(b), code sequences which actually include errors are found asfollows. Specifically, in FIG. 23( a), in 34 out of 40 patterns, therecorded pattern is detected with an anterior shift in part of “3T orlonger space, 2T mark, 2T space” by 1 bit. In FIG. 23( b), in 23 out of28 patterns, the recorded pattern is detected with a posterior shift inpart of “2T space, 2T mark, 3T or longer space” by 1 bit.

Thus, the large part of the errors are attributed to an anterior orposterior shift by 1 bit of a pattern represented by Table 3 whichincludes a consecutive sequence of “2T space-2T mark” or “2T mark-2Tspace”.

It is understood that the patterns represented by Table 3 above is acode sequence which readily causes a bit error due to opticalintersymbol interference or thermal interference in the case of highdensity recording such as 33.4 GB. Also, as for these patterns, in thecase of a consecutive pattern including the combination of “2T mark-2Tspace” as shown in FIG. 23( a), the reproduction signal includes ananterior error. In the case of a consecutive pattern including thecombination of “2T space-2T mark” as shown in FIG. 23( b), thereproduction signal includes a posterior error.

Therefore, the extended recording compensation is made using differentrecording compensation values for a case where a 2T mark is succeeded bya 2T space and preceded by a 3T or longer space and a case where a 2Tmark is succeeded by a 2T space and preceded by a 2T space, whereby thebit error can be ameliorated.

Likewise, the extended recording compensation is made using differentrecording compensation values for a case where a 2T mark is preceded bya 2T space and succeeded by a 3T or longer space and a case where a 2Tmark is preceded by a 2T space and succeeded by a 2T space, whereby thebit error can be ameliorated.

These examples are more specifically described below.

First, it is assumed that the mark length of an interested mark and thespace length of its immediately preceding space are the shortest lengths(2T) in encoded data. It is also assumed that the mark length of a markwith succeeding that space (second mark) is the shortest length (2T).The move amount of two or more consecutive pulse edges (e.g., dTF1 anddTF2) in the write pulse train in this case is described as “x1”. Themove amount of two or more consecutive pulse edges (e.g., dTF1 and dTF2)in the write pulse train under the circumstance where the length of thesecond mark is different from the shortest length (≧3T) is described as“y1”.

Further, it is assumed that the mark length of an interested mark andthe space length of its immediately succeeding space are the shortestlengths (2T) in encoded data. It is also assumed that the mark length ofa mark with preceding that space (third mark) is the shortest length(2T). The move amount of two or more consecutive pulse edges (e.g., dTE2and dTE3) in the write pulse train in this case is described as “x2”.The move amount of two or more consecutive pulse edges (e.g., dTE2 anddTE3) in the write pulse train under the circumstance where the marklength of the third mark is different from the shortest length (≧3T) isdescribed as “y2”.

Under the above assumptions, changing x1, x2, y1, and y2 so as to meetthe following formula is effective:(y1−x1)×(y2−x2)≦0.Specifically, moving the write pulse edge in opposite directionsdepending on whether the preceding mark is “2T” or “3T or longer” andwhether the succeeding mark is “2T” or “3T or longer”, according to theerror distribution, and performing the recording with a shift in theposition of the 2T mark while the width of the recording pulse at thepeak power level (top pulse width) is fixed, are especially effective.Such an arrangement enables reduction of intersymbol interference andthermal interference without changing the size of the record mark (2T).

Furthermore, a code sequence in which an error occurs is compared withoriginal data to detect the type and direction of the code sequence inwhich the error occurs, and a combination of code sequences which has ahighest frequency of occurrence or highest probability of occurrence ofbit errors is recording-compensated. Thereby, the bit error rate isfurther decreased, so that the reproduction signal quality can beimproved.

Also, x1, x2, y1, and y2 may be controlled so as to meet the followingformula:|y1−x1|=|y2−x2|.As a result, the half recording position of the 2T mark is shiftedequally to the anterior side and the posterior side. The average of therecording positions of the entire 2T mark remains the same even afterthis write pulse edge is shifted. Therefore, even when the changeamounts of the write pulse conditions (y1−x1, y2−x2) for the sequence ofa 2T mark, a 2T space with the preceding or succeeding 2T mark, and a 3Tor longer mark with the preceding or succeeding 2T space are varied, theabsolute values of the change amounts are maintained equal, and thechange is made in opposite directions. Thus, the phase change in the PLLas a whole is small, so that the detection error due to the phase shiftin the PLL can be reduced.

Here, in the case where the Euclidean distance of the state transitionpatterns that can take two state transition paths is 12, the targetvalue of the shift adjustment is not modified so that each patternbecomes 0. Instead, in the case where 4 code sequences of mark, space,mark, and space include two or more correct code sequences, the shiftadjustment may be carried out such that the average of the shift amountbecomes 0 in two or more code sequences. The transitions “S2k−7→S1k” and“S3k−5→S2k” in Table 3 each include a correct code sequence of “3T mark,2T space, 2T mark, 3T space”. One of the code sequences which are to becompared is “2T space, 2T mark, 2T space, 4T mark”, and the other is “4Tspace, 2T mark, 2T space, 2T mark”. Comparison with a code sequence of adifferent shift direction is carried out, and the adjustment is carriedout such that the average value of the shifts detected in the respectivepatterns becomes 0, whereby the shift deviation is effectivelycorrected, and intersymbol interference or thermal interference can bereduced.

Next, the record patterns are described. In general, as the code lengthincreases, the frequency (probability) of occurrence of the recordpatterns relative to the code length decreases. Specifically, thefrequency of occurrence is 2T>3T>4T> . . . >8T. For example,approximately, 2T is 38%, 3T is 25%, and 4T is 16%. Note that the codelength distribution of a 17PP-modulated record pattern which is used inrecording of common user data also depends on a non-modulated datasequence. In the case where recording is carried out under write pulseconditions varied using record patterns which have different frequenciesof occurrence of code lengths, and the recorded mark is read out and thedifference between two write pulse conditions is detected as an edgedeviation amount, the recording is affected by the above-describedfrequencies of occurrence of respective code lengths of the modulatedcodes, so that the phase which is supposed to be locked by the PLL issignificantly affected by a specific code length to vary. Especially inthe recording of a 2T mark which has the probability of occurrence of ⅓or higher, a change in the edge position of the 2T mark leads to achange in the average phase distribution of the total record marks.Accordingly, the phase which is supposed to be locked by the PLL isshifted. In the case where the edge position information of the recordmark is detected using a PLL clock, significant detection errors occurin the edge position information or in the phase components of marks inthe case of mark lengths which have relatively low frequencies ofoccurrence, especially in this embodiment, in the case of mark lengthsequal to 4T or longer.

The record patterns used for adjustment of 2T and 3T marks of thepresent embodiment are specific patterns in which the frequencies ofoccurrence of the code lengths from 2T to 8T are generally equal andwhich are DSV-controlled. By using the above-described specific patternswith equal frequencies of occurrence, the frequency of occurrence ofeach code length is equal to 1/7, so that the frequency of occurrence ofeach of 2T and 3T is 1/7, and the frequency of occurrence of 4T orlonger is 5/7. Thus, the frequency of occurrence of 4T or longer marksbecomes dominant. In this case, even when the write pulse conditions ofthe 2T and 3T marks are changed, the edge positions of the record marksof 4T or longer whose write pulse conditions are not changed do notvary. Thus, the phase change of the PLL as a whole is small, so that thedetection error due to the phase shift of the PLL can be reduced.

Signals which are to be pre-recorded may be produced by performing thefirst test writing using a code sequence from which the shortest marklength (2T) is excluded to obtain recording compensation values for thecode lengths of 3T or longer mark lengths, and then, performing thesecond test writing using a code sequence including a 2T signal toobtain recording compensation values for the code lengths including the2T signal. In an optical disc medium where the storage capacity per datarecording layer is 33.4 GB, the amplitudes of short marks and spaces inthe reproduction signal are extremely small. Under a circumstance wherein such an optical disc medium the record mark position of a 2T signalhas not been correctly recorded, correct positioning of long marks andspaces which are equal to or longer than 3T is sometimes difficult. Inthe case where a signal which includes an extremely large intersymbolinterference as described above is reproduced, recording of the signalmay be realized by first recording marks with the code length of 3Tw orlonger and correctly making recording compensation on the edge positionsof marks and spaces of 3Tw or longer, and then recording a signal whichincludes a 2Tw signal and correctly making compensation on the recordingpositions of the 2Tw marks and spaces. With such an arrangement,recording can be carried out more correctly and more efficiently, sothat the reproduction signal quality can be improved.

In the test recording, the record mark size and shift amounts of shortmarks, such as 2T and 3T marks, are different among the respectiverecording conditions. As the tap coefficients of an adaptiveequalization filter vary on every occasion of the test recording, theshift state of a read signal which depends on variations in thereproduction state in addition to variations in the recording state needto be additionally considered. Therefore, to correctly perform anadjustment of the shift caused by differences in recording conditions,in the case of making a recording adjustment, fixing the boost values ofthe reproduction equalizer or the tap coefficients of the adaptiveequalization filter in advance for adjustment of test recording orrecording compensation is rather preferable. This enables a preciseadjustment of the shift position of each pattern.

Next, the procedure of the extended recording compensation is describedwith reference to FIG. 24. FIG. 24 is a flowchart illustrating theprocedure of the extended recording compensation on an optical discmedium according to the present embodiment such that the write pulseconditions are optimized. A computer program which defines the processprocedure described in this flowchart is executed by a computer. Thecomputer and hardware required for that process operate as the opticalrecording/reproduction device shown in FIG. 1.

The first step is setting of the recording conditions. The write pulsecondition calculating section 110 sets recording conditions pre-recordedin the optical disc medium 101 or recording conditions stored in amemory of the optical recording device.

The second step is a writing step for adjustment of patterns which havethe code distance of 14. The recording compensation section 112 controlsthe laser driving section 113 and the light emitting section 102 tocarry out test recording in a predetermined track on the optical discmedium 101 under the recording conditions set in the first step. Thethird step is reproduction of a written signal and detection of an edgeshift with the code distance of 14. The shift detecting section 109detects 18 edge shift patterns shown in Table 1 according to theabove-described edge shift detection method.

The fourth step is the step of determining whether or not the edge shiftamount of the code distance of 14 shown in Table 1 is equal to orsmaller than a desired value. If the edge shift amount is suppressed tobe equal to or smaller than the desired value, the procedure advances tothe next step. On the other hand, if the edge shift amount is notsuppressed to be equal to or smaller than the desired value, theprocedure returns to the above-described second step. The write pulsecondition calculating section 110 sets the recording compensationconditions according to the edge shift amount for another test recordingsession.

The fifth step is detection of a phase shift of the code distance of 12shown in Table 2 and Table 3. The shift detecting section 109 detects 18patterns of phase shift shown in Table 2 and Table 3 according to theabove-described shift detection method.

Note that, as for the code distance of 14, an “edge shift” is detected,but as for the code distance of 12, a “phase shift” is detected. Thereasons for this are described below. Adjustment of the patterns withthe code distance of 14 is realized by modifying the write pulse tochange the “edge position” of a mark at the leading or trailing end. Assuch, it is necessary to detect an edge shift of a test-recorded mark.On the other hand, adjustment of the patterns with the code distance of12 is not realized by adjusting the leading end position or trailing endposition of a mark but by changing the recording positions of aplurality of consecutive marks and spaces. Therefore, it is necessary todetect test-recorded marks and spaces as a whole. In this specification,the difference between the detection targets is identified by usingdifferent terms, “edge shift” and “phase shift”. Note that using thesedifferent terms is for the sake of convenience and therefore should notbe strictly interrupted. This is because the “phase shift” has a broadermeaning that refers to detection of an edge shift in the respectivetest-recorded marks.

The sixth step is the step of determining whether or not the edge shiftamount of the code distance of 12 shown in Table 2 and Table 3 issuppressed to be equal to or smaller than a desired value. If the phaseshift amount is suppressed to be equal to or smaller than the desiredvalue, the adjustment procedure ends. If the phase shift amount is notsuppressed to be equal to or smaller than the desired value, theadjustment procedure advances to the next step.

The seventh step is the writing step for adjustment of the patterns withthe code distance of 12. The write pulse condition calculating section110 sets the recording compensation conditions according to a phaseshift result detected in the fifth step, and test recording is carriedout in a predetermined track on the optical disc medium. Then, theprocedure returns to step 5.

The procedure of the present embodiment shown in FIG. 24 includesperforming test recording in a test recording area to determinerecording compensation values. However, recording in the test recordingarea is impossible in some devices, such as a master-manufacturingexposure apparatus. In such a case, test recording may be carried out onanother material disc of the optical disc medium to determine therecording conditions before a master disc cutting process.

The optical disc medium of the present embodiment includes optical discmedia of such a type that the effects of thermal interference greatlyvary according to the lengths of spaces that precede and succeed themark. When writing is performed on an optical disc medium of such atype, it is necessary to change the write pulse conditions according notonly to the mark length but also to the lengths of the preceding andsucceeding spaces. Note that, however, when the lengths of spacespreceding and succeeding the mark are considered, the number ofcombinations of the write pulse conditions increases two-dimensionally,and accordingly, the number of parameters adjusted via thetest-recording increases. As such, the period of time required forlearning increases, and a larger number of tracks in the recordingcondition learning area are consumed. In optical disc media which allowrecording only once in the same area, such as write-once disc media, thenumber of learning sessions is limited because the recording conditionlearning area only has a limited number of tracks, and consuming a largenumber of tracks in one learning session is not favorable. As such, awrite pulse condition optimizing method of the present embodimentincludes adjustment of the write pulse conditions according toclassification for respective mark lengths. In the case of an opticaldisc medium having properties which need no compensation according tothe lengths of spaces preceding and succeeding the mark, the write pulseconditions are corrected according only to the mark length, withoutperforming an unnecessary adjustment step. In this way, by limiting thecorrection of the write pulse conditions to the adjustment forrespective mark lengths, the time for the adjustment can be shortened,and the signal quality of recorded marks can efficiently be improved.

On the other hand, in the case of an optical disc medium which needsadjustment of the write pulse conditions according to the lengths ofspaces immediately preceding and succeeding a mark and the lengths ofmarks with the preceding space and succeeding space, or in the casewhere correction of the write pulse conditions for respective marklengths and respective space lengths of the preceding and succeedingspaces cannot solely provide sufficient compensation for deviations ofthe recorded marks, the write pulse conditions are adjusted accordingnot only to the lengths of spaces preceding and succeeding the mark butto the lengths of marks preceding and succeeding the spaces, so that thesignal quality of recorded marks can be improved.

Also, classification-related information, such as whether or not theextended recording compensation is made, the number of classes of marklengths and space lengths for the recording compensation, whether or notthe preceding-mark compensation is necessary, whether or not thesucceeding-mark compensation is necessary, the number of classes, etc.,may be preliminarily stored in a predetermined area of an optical discmedium. The predetermined area may be the initial value storage area1003 (FIG. 2) which is provided in a read-in area at the inner perimeterof the optical disc medium. This enables correction of the write pulseconditions according to the properties of the optical disc medium,without performing unnecessary adjustment steps. In the case where thenumber of classes for the recording compensation, or whether or not thepreceding- or succeeding-mark compensation is necessary, is thus knownin advance, the time for adjustment can be shortened, and the signalquality of recorded marks can efficiently be improved.

After the learning in the optical disc drive, classification-relatedinformation, such as whether or not the extended recording compensationis made, the number of classes of mark lengths and space lengths for therecording compensation, whether or not the preceding-mark compensationis necessary, whether or not the succeeding-mark compensation isnecessary, the number of classes, etc., may be recorded in apredetermined area. The predetermined area may be the initial valuestorage area 1003 which is provided in a read-in area at the innerperimeter of the optical disc medium. This enables correction of thewrite pulse conditions according to the properties of the optical discmedium, without performing unnecessary adjustment steps at the nextstartup. In the case where the number of classes for the recordingcompensation or whether the preceding- or succeeding-mark compensationis necessary is thus known in advance, the time for adjustment can beshortened, and the signal quality of recorded marks can efficiently beimproved.

A reproduction device or a reproduction method of the present inventionincludes a reproduction section or a reproduction step for irradiatingan optical disc medium with laser light for reproduction of information.Furthermore, as previously described, the reproduction device or methodmay include a section or step of retrieving the classification-relatedinformation recorded in a predetermined area of an optical disc medium(for example, the initial value storage area 1003), such as whether ornot the extended recording compensation is made, the number of classesof mark lengths and space lengths for the recording compensation,whether or not the preceding- and succeeding-space compensation isnecessary, whether or not the preceding-mark compensation is necessary,whether or not the succeeding-mark compensation is necessary, the numberof classes, etc. This enables correction of the write pulse conditionsaccording to the properties of the optical disc medium, withoutperforming unnecessary adjustment steps at the next startup. In the casewhere the number of classes for the recording compensation or whether ornot the preceding- or succeeding-mark compensation is necessary is thusknown in advance, the time for adjustment can be shortened, and thesignal quality of recorded marks can efficiently be improved.

Although the description of the present embodiment has been providedwith an example of the PR(1,2,2,2,1)ML method, the present invention isnot limited to this example. A combination of PRML methods which iscapable of embodying the concept of the present invention may beselected.

Although the embodiment of present invention which is described hereinis the optical recording method, it may be an opticalrecording/reproduction method which includes recording and reproductionoperations.

Although the embodiment of the present invention has been described withan example of an optical recording/reproduction device and a write-onceoptical disc medium, the present invention is not limited to thisexample. The present invention is useful for a master-manufacturingexposure apparatus for rewritable optical disc media or read-onlyoptical disc media. For example, in a mastering step included in theprocess of manufacturing a read-only optical disc medium, even whencutting of a material disc is carried out using a laser beam at thewavelength of about 400 nm on an inorganic resist coating, the effectsof the optical recording method of the present embodiment areparticularly achieved.

FIG. 25 shows such a material disc cutting apparatus. The material disccutting apparatus includes an objective lens 2203, a motor 2204, a lightmodulator 2205, a laser 2706, a recording compensation circuit 2207, amemory 2208, a record pattern generation circuit 2209, and a turntable2210.

As shown in FIG. 25, the memory 2208 contains the extended recordingcompensation values shown in FIG. 10 which have been obtained by thedevice of FIG. 1. First, information about the adjustment method fordTF1, dTF2, dTF3, dTE1, dTE2, and dTE3 are retrieved from the memory2208. In the record pattern generation circuit 2209, modulation,addition of ECC, scrambling, etc., are performed, whereby it isconverted into binary data for recording (NRZI signal). The laser beamemitted from the laser 2206 is modulated in terms of the emission powerby the light modulator 2205 according to the output signal from therecording compensation circuit 2207 and is directed via the objectivelens 2203 onto an inorganic resist coating 2202 applied over a glassmaterial disc 2201. In this step, the binary recording is realized bythe presence and absence of irradiation. Thereafter, portions irradiatedwith the laser are molten away, and sputtering of a metal, such asnickel, is performed, whereby a metal stamper having concavity/convexitypits is fabricated. The metal stamper is used as a mold to form a discsubstrate, and a recording film and other elements are formed on thedisc substrate. The two substrates which have a recording film formed atleast on one side are combined into one disc.

When cutting of a material disc is performed using an electron beam,pits can be formed with a high density because of its short wavelength.However, the time required for the cutting is considerably long ascompared with the case of a laser beam, and accordingly, the productioncost of a master disc of an optical disc medium increases. By using anoptical information device of the present embodiment, cutting of amaterial disc is performed using a laser beam, so that inexpensiveoptical disc media can be provided.

An optical disc medium manufacturing method of the present embodimentwhich uses the above-described master-manufacturing exposure apparatusmay include the step of forming a predetermined area in an optical discmedium for storing information relating to classification which isnecessary for the above-described extended recording compensation. Theinformation relating to classification may include whether or not theextended recording compensation is made, the number of classes of marklengths and space lengths for the recording compensation, whether or notthe preceding-mark compensation is necessary, whether or not thesucceeding-mark compensation is necessary, the number of classes, etc.The predetermined area may be the initial value storage area 1003 whichis provided in a read-in area at the inner perimeter of the optical discmedium. Such a manufacturing method enables recording ofclassification-related information in an optical disc medium. Thisenables correction of the write pulse conditions according to theproperties of the optical disc medium, without performing unnecessaryadjustment steps. In the case where the number of classes for therecording compensation or whether or not the preceding- orsucceeding-mark compensation is necessary is thus known in advance, thetime for adjustment can be shortened, and the signal quality of recordedmarks can efficiently be improved.

Next, FIG. 26 is a schematic view of a stack configuration of athree-layer optical disc medium of the present embodiment. In thethree-layer optical disc medium, a substrate 2603, a data recordinglayer L0 2600 (“L0” is an abbreviation for “Layer0”), a data recordinglayer L1 2601, a data recording layer L2 2602, and a cover layer 2606are disposed in this order. The laser light comes in from the coverlayer 2606 side toward the substrate 2603.

The thickness of the substrate 2603 is approximately 1.1 mm, thethickness of the cover layer 2606 is at least 53 μm or more, datarecording layers L0, L1, and L2 are separated by transparent spacelayers 2604 and 2605.

In the present embodiment, in a specific example described herein, thethickness of the cover layer 2606 is 57 μm, the thickness of a spacelayer 2605 between L2 and L1 is 18 μm, and the thickness of a spacelayer 2604 between L1 and L0 is 25 μm. The intervals between therespective data recording layers separated by the space layers arepreferably designed such that interference of diffracted light from therespective data recording layers (interlayer interference) decreases.The present invention is not limited to the interlayer distances definedby the above-described thicknesses of the space layers. Especially inthe case of a layered disc, the L2 and L1 layers need to transmit lightto inner layers and therefore need to be designed to have atransmittance as high as 55% to 65%.

In the case where writing is performed on a recording medium which has arecording layer of such a high transmittance with a high recordingdensity of mark lengths that are beyond the optical resolution, thethicknesses of recording films of the respective data recording layers,reflection films, dielectric films, etc., need to be decreased in orderto ensure the high transmittance. Therefore, diffusion of heat to thedielectric films and reflection films provided on the upper and lowersides of the recording film is smaller whereas diffusion of heat withinthe plane of the recording film is larger. Specifically, in recording ofmarks, the recording edge positions of marks deviate due to thermalinterference. The extended recording compensation of the presentinvention is a recording compensation method especially effective in thecase where very small marks that are beyond the optical resolution arerecorded on a recording medium having such a high transmittance layer.

Note that, although an optical pickup head which is the same as thosecommonly used in conventional BDs is used in the examples describedherein, the optical pickup head may have any configuration so long as itis configured to emit a beam on an optical storage medium and output asignal according to a beam reflected by the optical storage medium.

INDUSTRIAL APPLICABILITY

The optical recording/reproduction method and opticalrecording/reproduction device according to the present invention, whichare employed for optical disc media, are advantageously capable of highdensity recording on optical recording media, and are applicable to theelectric and electronic device industries including digital homeappliances, information processing devices, etc.

REFERENCE SIGNS LIST 101 optical disc medium 102 light emitting section103 preamplifying section 105 waveform equalizing section 108 PRMLprocessing section 109 shift detecting section 110 write pulse conditioncalculating section 111 recording pattern generating section 112recording compensation section 113 laser driving section

The invention claimed is:
 1. An optical recording method for recordinginformation by irradiating an optical disc medium with a modulated writepulse train of laser light variable over a plurality of power levelssuch that a plurality of marks are formed on the optical disc medium,edge positions of each of the marks and a space between adjacent two ofthe marks being utilized for recording of the information, the methodcomprising the steps of: encoding record data to generate encoded datawhich is a combination of marks and spaces; classifying the encoded dataaccording to a combination of a mark length of a mark, a space length ofa first space that immediately precedes the mark, and a space length ofa second space that immediately succeeds the mark; generating a writepulse train for forming the mark, in which at least one of a leading endedge position, a trailing end edge position, and a pulse width of thewrite pulse train is changed according to a result of theclassification; and irradiating the optical disc medium with thegenerated write pulse train to form the plurality of marks on theoptical disc medium, wherein the space length of the first space isclassified in M space length classes (M is an integer equal to orgreater than 1) and the space length of the second space is classifiedin N space length classes (N is an integer equal to or greater than 1),and wherein: in the case of one of the leading end edge position and thepulse width is changed, the step of generating the write pulse trainchanges one of the leading end edge position and the pulse widthaccording to the result of the classification so that M is greater thanN; and in the case of the trailing end edge position is changed, thestep of generating the write pulse train changes the trailing end edgeposition according to the result of the classification so that N isgreater than M.
 2. The optical recording method of claim 1, wherein thestep of classifying includes classifying the encoded data according to acombination of a mark length of a shortest mark, the space length of thefirst space, and the space length of the second space.
 3. The opticalrecording method of claim 1, wherein the step of classifying includesclassifying the encoded data according to a combination of the followingconditions: the mark length of the mark; whether the space length of thefirst space is “n” or “n+1 or longer”; and whether the space length ofthe second space is “n” or “n+1 or longer”, where n is a shortest spacelength.
 4. The optical recording method of claim 1, wherein the step ofclassifying includes classifying the encoded data by space length intofour space length classes for the first space, “n”, “n+1”, “n+2”, and“n+3 or longer”, and two space length classes for the second space, “n”and “n+1 or longer”, where n is a shortest space length, and the step ofgenerating includes changing the leading end edge position of the writepulse train according to the result of the classification.
 5. Theoptical recording method of claim 1, wherein the step of classifyingincludes classifying the encoded data by space length into two spacelength classes for the first space, “n” and “n+1 or longer”, and fourspace length classes for the second space, “n”, “n+1”, “n+2”, and “n+3or longer”, where n is a shortest space length, and the step ofgenerating includes changing the trailing end edge position of the writepulse train according to the result of the classification.
 6. Theoptical recording method of claim 1, wherein the step of classifyingincludes classifying the encoded data by space length into four spacelength classes for the first space, “n”, “n+1”, “n+2”, and “n+3 orlonger”, and two space length classes for the second space, “n” and “n+1or longer”, where n is a shortest space length, and the step ofgenerating includes changing the pulse width of the write pulse trainaccording to the result of the classification.
 7. The optical recordingmethod of claim 1, wherein the step of classifying includes, if the marklength of the mark is longer than a shortest mark length, classifyingthe encoded data according to at least any one of a combination of themark length and the first space length and a combination of the marklength and the second space length.
 8. The optical recording method ofclaim 1, further comprising the steps of: generating an analog signalfrom the optical disc medium and generating a digital signal from theanalog signal; reshaping a waveform of the digital signal; maximumlikelihood decoding the reshaped digital signal based on a PRML (PartialResponse Maximum Likelihood) method; generating a binary signal whichrepresents a result of the maximum likelihood decoding; and detecting ashift amount in the waveform of the reshaped digital signal based on thereshaped digital signal and the binary signal, wherein the step ofgenerating the write pulse train includes changing, based on a result ofthe detection of the shift amount, at least one of the leading end edgeposition, the trailing end edge position, and the pulse width of thewrite pulse train for the formation of the plurality of marks.
 9. Theoptical recording method of claim 8, wherein the step of detectingincludes detecting the shift amount in the waveform of the digitalsignal by a comparison of the encoded data and the binary signal, andthe step of generating the write pulse train includes changing at leastone of the leading end edge position, the trailing end edge position,and the pulse width of the write pulse train.
 10. The optical recordingmethod of claim 1, wherein the step of generating the write pulse trainincludes changing a position of at least one of first to third pulseedges counted from the leading end and first to third pulse edgescounted from the trailing end according to the result of theclassification.
 11. The optical recording method of claim 1, wherein thefollowing formula holds:ML<λ/NA×0.26 where λ is a wavelength of the laser light, NA is anumerical aperture of an objective lens, and ML is a shortest marklength.
 12. The optical recording method of claim 11, wherein theshortest mark length ML is 0.128 μm or less.
 13. The optical recordingmethod of claim 11, wherein the laser light wavelength λ is in the rangeof 400 nm to 410 nm, and the NA is in the range of 0.84 to 0.86.
 14. Anoptical recording apparatus for recording information by irradiating anoptical disc medium with a modulated write pulse train of laser lightvariable over a plurality of power levels such that a plurality of marksare formed on the optical disc medium, edge positions of each of themarks and a space between adjacent two of the marks being utilized forrecording of the information, the apparatus comprising: an encodingsection configured to encode record data to generate encoded data whichis a combination of marks and spaces; a classification sectionconfigured to classify the encoded data according to a combination of amark length of a mark, a space length of a first space that immediatelyprecedes the mark, and a space length of a second space that immediatelysucceeds the mark; a recording waveform generating section configured togenerate the write pulse train for forming the mark in which at leastone of a leading end edge position, a trailing end edge position, and apulse width of the write pulse train is changed according to the resultof the classification; and a laser driving section configured toirradiate the optical disc medium with the generated write pulse trainto form the plurality of marks on the optical disc medium, wherein thespace length of the first space is classified in M space length classes(M is an integer equal to or greater than 1) and the space length of thesecond space is classified in N space length classes (N is an integerequal to or greater than 1), and wherein: in the case of one of theleading end edge position and the pulse width is changed, the recordingwaveform generating section changes one of the leading end edge positionand the pulse width according to the result of the classification sothat M is greater than N; and in the case of the trailing end edgeposition is changed, the recording waveform generating section changesthe trailing end edge position according to the result of theclassification so that N is greater than M.
 15. The optical recordingapparatus of claim 14, further comprising: a PRML processing sectionconfigured to receive a digital signal generated from an analog signalreproduce from an optical disc medium, to reshape a waveform of thedigital signal, and to maximum likelihood decode the reshaped digitalsignal based on a PRML (Partial Response Maximum Likelihood) method; ashift detecting section configured to detect a shift amount in thewaveform of the digital signal based on a binary signal which representsa result of the maximum likelihood decoding and the reshaped digitalsignal; and a recording compensation section configured to change, basedon a result of the detection of the shift amount, at least one of theleading end edge position, the trailing end edge position, and the pulsewidth of the write pulse train for the formation of the plurality ofmarks.
 16. A master-manufacturing exposure apparatus for recordinginformation by irradiating an optical disc medium which is aresist-coated material disc with a modulated write pulse train of laserlight variable over a plurality of power levels such that a plurality ofmarks are formed on the optical disc medium, edge positions of each ofthe marks and a space between adjacent two of the marks being utilizedfor recording of the information, the apparatus comprising: an encodingsection configured to encode record data to generate encoded data whichis a combination of marks and spaces; a classification sectionconfigured to classify the encoded data according to a combination of amark length of a mark, a space length of a first space that immediatelyprecedes the mark, and a space length of a second space that immediatelysucceeds the mark; a recording waveform generating section configured togenerate the write pulse train for forming the mark in which at leastone of a leading end edge position, a trailing end edge position, and apulse width of the write pulse train is changed according to a result ofthe classification; and a laser driving section configured to irradiatethe optical disc medium with the generated write pulse train to form theplurality of marks on the optical disc medium, wherein the space lengthof the first space is classified in M space length classes (M is aninteger equal to or greater than 1) and the space length of the secondspace is classified in N space length classes (N is an integer equal toor greater than 1), and wherein: in the case of one of the leading endedge position and the pulse width is changed, the recording waveformgenerating section changes one of the leading end edge position and thepulse width according to the result of the classification so that M isgreater than N; and in the case of the trailing end edge position ischanged, the recording waveform generating section changes the trailingend edge position according to the result of the classification so thatN is greater than M.
 17. An optical disc medium in which information isto be recorded based on an optical recording method for recordinginformation by irradiating the optical disc medium with a modulatedwrite pulse train of laser light variable over a plurality of powerlevels such that a plurality of marks are formed on the optical discmedium, edge positions of each of the marks and a space between adjacenttwo of the marks being utilized for recording of the information,wherein the optical recording method includes the steps of: encodingrecord data to generate encoded data which is a combination of marks andspaces; classifying the encoded data according to a combination of amark length of a mark, a space length of a first space that immediatelyprecedes the mark, and a space length of a second space that immediatelysucceeds the mark; generating a write pulse train for forming the mark,in which at least one of a leading end edge position, a trailing endedge position, and a pulse width of the write pulse train is changedaccording to a result of the classification; and irradiating the opticaldisc medium with the generated write pulse train to form the pluralityof marks on the optical disc medium, wherein the space length of thefirst space is classified in M space length classes (M is an integerequal to or greater than 1) and the space length of the second space isclassified in N space length classes (N is an integer equal to orgreater than 1), and wherein: in the case of one of the leading end edgeposition and the pulse width is changed, the step of generating thewrite pulse train changes one of the leading end edge position and thepulse width according to the result of the classification so that M isgreater than N; and in the case of the trailing end edge position ischanged, the step of generating the write pulse train changes thetrailing end edge position according to the result of the classificationso that N is greater than M, the optical disc medium comprising apredetermined area, wherein information about the classification to beused for the classification in the step of classifying is contained inthe predetermined area.
 18. A method for reproducing information from anoptical disc medium in which the marks are to be recorded based on anoptical recording method, for recording information by irradiating theoptical disc medium with a modulated write pulse train of laser lightvariable over a plurality of power levels such that a plurality of marksare formed on the optical disc medium, edge positions of each of themarks and a space between adjacent two of the marks being utilized forrecording of the information, wherein the optical recording methodincludes the steps of: encoding record data to generate encoded datawhich is a combination of marks and spaces; classifying the encoded dataaccording to a combination of a mark length of a mark, a space length ofa first space that immediately precedes the mark, and a space length ofa second space that immediately succeeds the mark; generating a writepulse train for forming the mark, in which at least one of a leading endedge position, a trailing end edge position, and a pulse width of thewrite pulse train is changed according to a result of theclassification; and irradiating the optical disc medium with thegenerated write pulse train to form the plurality of marks on theoptical disc medium, wherein the space length of the first space isclassified in M space length classes (M is an integer equal to orgreater than 1) and the space length of the second space is classifiedin N space length classes (N is an integer equal to or greater than 1),and wherein: in the case of one of the leading end edge position and thepulse width is changed, the step of generating the write pulse trainchanges one of the leading end edge position and the pulse widthaccording to the result of the classification so that M is greater thanN; and in the case of the trailing end edge position is changed, thestep of generating the write pulse train changes the trailing end edgeposition according to the result of the classification so that N isgreater than M, wherein the optical disc medium including apredetermined area, in which information about the classification to beused for the classification in the step of classifying is contained, themethod for reproducing information comprising the step of: reproducingthe information contained in the optical disc medium by irradiating theoptical disc medium with laser light; and reading the information aboutthe classification to be used for the classification from thepredetermined area.